Android : how to back to previous fragment on pressing manually back button

I have one activity and multiple fragments in my app. i want to back one by one fragments when pressing back button which in all fragments.

i used this code segment but when pressing back button it comes to main activity without back one by one. Also i want to change the icon when it's comes to the main activity.(msg_alert)

FragmentManager fm = MainActivity.this
                    .getSupportFragmentManager();
            FragmentTransaction ft = fm.beginTransaction();
            Fragment fragment = new MainMenuLayout();
            ft.replace(R.id.activity_main_content_fragment, fragment);
            ft.commit();
            btnBack.setVisibility(View.VISIBLE);
            btnBack.setImageResource(R.drawable.msg_alert);
            tvTitle.setText("Layout 0");