Android : How to change menu icon

I have the following menu that i declare in Main activity :

public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);

 //... populate with menu.add()

}

The menu icon looks like 3 dotts and it's position is on the action bar on the right side. In my app i use Fragments and i want to change the menu icon ( the icon i press to open de menu items ) depending on the fragment it's in front.

How can i do that programmatically?

Also on some of my fragments i don't want the menu to appear. For this i use inside those fragments :

public void onCreateOptionsMenu(Menu menu, MenuInflater inflater)
{
    super.onCreateOptionsMenu(menu, inflater);
    menu.clear();
}

And i try to find a way using the menu var to change the icon of the menu. But i did not find a way.

So.... can you please show me how to change the menu icon programmatically?

Thanks,