You can change the drop down navigation menu in thesis Wordpress theme. So to do this first go to word press admin and click add new to add a new page after that create some more pages. You have to select your page in parent menu under which you want to create that pages like service parent and then click publish. Now go to thesis option and click thesis option and go to navigation menu. There you can see all the pages which you have created now you have to select the pages you want and save it. Now go to your site and check the drop down menu.