My wife's phone is running 3.1.2 and was unlocked using Blackra1n.

How do I go about upgrading her phone to 4? She does NOT want it to be unlocked/jailbroken anymore, so that doesn't matter. She just wants the standard Apple software. What happens if I just plug it up and upgrade? Or do I need to erase everything off of it first?

Sorry in advance for my lack of knowledge on the issue.