How do I unjailbreak my iPhone 4? IOS 4

[iMore Question]

So I got a hand-me-down iPhone 4 (not 4s) and it is jailbroken and not updated which really annoys me, I have tried to plug it into my desktop computer and erase all the data and update it to IOS 7 and unjailbreak it. Although, It's not working, when I go to settings and do the erase iPhone option, the loading sign stays spinning for 12 hours and has not stopped. iTunes also says that there's a network error. Please help, I really want to update my iPhone!

 

[rdiddy_25]

You have to place it into DFU mode first, then restore as new thru iTunes. If unsure how to do that, click the link in my signature.