factory reset

Greetings,

I have an iPhone 3GS and had it unlocked it through AT&T but they advised it would not be fully unlocked until I did a complete factory reset. I am using the latest version of iTunes but the display is very different and I am just trying to get to the factory reset option so that I can sell it as I now have the iPhone 5. Any assistance would be appreciated as I have checked all over online with no success with this version of the software. It used to come up directly to the home screen with a menu on the right showing the phone and when I clicked it the menu showed me the options for backup/restore/restore to factory defaults but that is no longer the case. Now the menus are all at the top with no choice for me to do what I am trying.

I am sure this is a simple solution -

Thanks in advance ..