how so i replace my inbuilt menubar

I am using wp version 3.0.1 and i tried with many themes to find menubar.php but i cant find it. i want to change my menubar according to me. but could not find that code in theme. bcz when i create a page and wanted to display it as a home page. one more page is to display and older home page is also there. how can i remove it from my site.

plz help me.