If you have a jailbroken iPhone and the jailbreaking was done with the same computer that you are trying to update the firmware from, then you may get a error 3194 when iTunes tries to verify the firmware version. To solve this:
- Open C:\Windows\System32\drivers\etc\hosts with notepad
- See if there are any lines in there that contains a reference to gs.apple.com
- Put a ‘#’ (without quote) in front of such line(s)
- Try updating again