Hi I'm trying to update my iphone 3GS to the new operating system (OS 4.0). I jailbroke it using pwange back when it was running 3.0 but have since lost the ipsw files. What is my best way to update to 4.0? I've tried downloading an ipsw for the previous update (3.1) but it won't let me restore to that - says apple doesn't recognise it. I changed my root password previously, is this the problem? I'd also like to JB it again when I do upgrade - can it be done at the same time so I don't lose apps and settings? Thanks for your help - I'm completely reliant on my phone for work (and life) and nervous that I might screw it all up!