Changing Blender's UI with Python?

I have a question. How can I change Blender’s menus, the ones on the top that say File, Render, Game, etc?

RMB on the area you want to change and select ‘Edit Source’, you will see a message at the top of the blender interface saying the name of the .py file that creates that interface element. Open a text editor window in blender and open the appropriate .py file from the drop down list

Okay, thanks! It worked.