You may want to turn off the main navigation bar completely. Perhaps your site does not go any deeper than the home page, or you want the main navigation bar gone for some other design reason. Here's how to turn it off.
Go to Menus Admin Page
Go to the Express toolbar and select Structure.
Select Menus from the list of options.
Click the Settings tab in the upper right.
Turn Off Main Links
In the drop-down Source for the Main links, choose No Main links.