Turning off Drop Down Menu in Twenty Ten

Hi, I am completely new to wordpress and I am trying to use it as a CMS to create a prototype website.

I have currently created a child theme of the theme twenty ten and have added a number of pages and sub pages. When I add the sub pages they appear as drop down items on the main navigation.. is there anyway to turn the drop down off as I have already used a widget which enables the sub menu to be displayed on the left hand side therefore i dont need submenu items in two locations.

Thanks