Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
You can't properly restore, you can uninstall cydia or whatever depending how you jailbroke, but the only way to really do it is restore your device,
 
Well, I've (kind of) found a solution. I'm going to an Apple Store and am going to have them do a factory restore for me.
 
hold down the power and home button for like 25 seconds or though, but you have to restore when you're done. Do that before you go to the apple store, or else they will see you're jailbroken and they won't do it
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.