I thought that it is impossible for a free WordPress account to have your menu in drop down style. I been searching ways on how to do it but i landed most of the forums on the wordpress.org which discussed that, it could be applicable if you put plug-ins in the blog. Unfortunately free WordPress blog was limited to this certain access unless you have your own domain name and paid web hosting. Upon several attempt and deep searching, i found two ways of doing it without the need of plug-ins. You can drag your categories in the menu bar or you can use us Pages . You can refer to my tutorial for detailed instructions.
Or you cant try this one