Android : Person Detail App

I am quite new to programming Android (7 months), and I am having a problem with creating an app. What I am trying to do is create a "Person Detail" test app for my own Android learning, by having EditText on the Main Activity with TextViews next to them (displaying default values at first), open up another activity called EditData (with a button on the main) which displays the values the user entered into the EditText (via Parcelable), return back to the Main Activty (via another button) and have those entered values displayed in the TextViews next to the EditText (upon a "Update Info" button click) instead of the default ones. I have managed to get everything working right except for displaying the changed values. Everything checks out, no errors in LogCat, but when the user / I clicks the update button, what shows are the default values. Can someone help me? Here is my Main Activity code:

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
    final Person firstPerson = new Person();
    TextView displayName, displayAge, displayHeight, displayWeight;
    EditText editName, editAge, editHeight, editWeight;
    Button editActivity, update;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);
    instantiateUi();
    editActivity.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            firstPerson.setPersonName(editName.getText().toString());
            firstPerson.setPersonAge(Integer.parseInt(editAge.getText().toString()));
            firstPerson.setPersonHeight(Integer.parseInt(editHeight.getText().toString()));
            firstPerson.setPersonWeight(Integer.parseInt(editWeight.getText().toString()));
            Intent editIntent = new Intent(MainActivity.this, EditData.class);
            editIntent.putExtra("First_Person_Data", firstPerson);
            MainActivity.this.startActivity(editIntent);
        }
    });
    update.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            displayName.setText(firstPerson.getPersonName());
            displayAge.setText(String.valueOf(firstPerson.getPersonAge()));
            // String.valueOf is needed to set int for TextViews
            displayHeight.setText(String.valueOf(firstPerson.getPersonHeight()));
            displayWeight.setText(String.valueOf(firstPerson.getPersonWeight()));
        }
    });
}

private void instantiateUi() {
    editName = (EditText)findViewById(R.id.edit_name);
    editAge = (EditText)findViewById(R.id.edit_age);
    editHeight = (EditText)findViewById(R.id.edit_height);
    editWeight = (EditText)findViewById(R.id.edit_weight);
    displayName = (TextView)findViewById(R.id.display_name);
    displayAge = (TextView)findViewById(R.id.display_age);
    displayHeight = (TextView)findViewById(R.id.display_height);
    displayWeight = (TextView)findViewById(R.id.display_weight);
    editActivity = (Button)findViewById(R.id.edit_activity);
    update = (Button)findViewById(R.id.update_info);

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main_menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.action_settings:
            break;
        default:
            return super.onOptionsItemSelected(item);
    }
    return true;
}
}    

My EditData activity code:

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class EditData extends ActionBarActivity {
    TextView changedName, changedAge, changedHeight, changedWeight;
    Button MainActivity;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.edit_activity);
    Person incomingObject = getIntent().getParcelableExtra("First_Person_Data");
    instantiateUi();
    changedName.setText(incomingObject.getPersonName());
    changedAge.setText(String.valueOf(incomingObject.getPersonAge()));
    changedHeight.setText(String.valueOf(incomingObject.getPersonHeight()));
    changedWeight.setText(String.valueOf(incomingObject.getPersonWeight()));
    MainActivity.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent EditActivity = new Intent(EditData.this, MainActivity.class);
            EditData.this.startActivity(EditActivity);
        }
    });
}

private void instantiateUi() {
    changedName = (TextView)findViewById(R.id.changed_name);
    changedAge = (TextView)findViewById(R.id.changed_age);
    changedHeight = (TextView)findViewById(R.id.changed_height);
    changedWeight = (TextView)findViewById(R.id.changed_weight);
    MainActivity = (Button)findViewById(R.id.main_activity);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.edit_data_menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}    

And my Parcelable class used for transferring data values:

import android.os.Parcel;
import android.os.Parcelable;

public class Person implements Parcelable{
    String personName;
    int personAge, personHeight, personWeight;

public Person(){
    personName = "No Name!";
    personAge = 0;
    personHeight = 0;
    personWeight = 0;
}

public Person(String pName, int pAge, int pHeight, int pWeight) {
    personName = pName;
    personAge = pAge;
    personHeight = pHeight;
    personWeight = pWeight;
}

public Person(Parcel in) {
    personName = in.readString();
    personAge = in.readInt();
    personHeight = in.readInt();
    personWeight = in.readInt();
}

public String getPersonName() {
    return personName;
}

public void setPersonName(String personName) {
    this.personName = personName;
}

public int getPersonAge() {
    return personAge;
}

public void setPersonAge(int personAge) {
    this.personAge = personAge;
}

public int getPersonHeight() {
    return personHeight;
}

public void setPersonHeight(int personHeight) {
    this.personHeight = personHeight;
}

public int getPersonWeight() {
    return personWeight;
}

public void setPersonWeight(int personWeight) {
    this.personWeight = personWeight;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(personName);
    dest.writeInt(personAge);
    dest.writeInt(personHeight);
    dest.writeInt(personWeight);
}

public static final Parcelable.Creator<Person> CREATOR =
        new Parcelable.Creator<Person>() {
            @Override
            public Person createFromParcel(Parcel in) {
                return new Person(in);
            }

            @Override
            public Person[] newArray(int size) {
                return new Person[size];
            }
        };
}    

Sorry if there are problems, this is my first question and I would very much appreciate what help you can give to a noob C0D3R :P