Need answers regarding upgrading my jailbroken iphone 3gS from 3.1.3 to 4.2.1

[cdy4946]

Okay, I've found a few threads dealing with this but none of them were exactly specific to my situation. I have an iPhone 3GS running version 3.1.3, firmware 05.12.01. I jailbroke it a while ago with spirit jailbreak, and havent updated it since then. I'd like to completely wipe my phone clean, and then update it to v4.2.1. I've already downloaded the 4.2.1 file from this site, but i'm not sure how to use it to update my phone to 4.2.1. Also I plan on jailbreaking it with redsnow 4.2.1 once it's updated. What should I do?

thanks for taking the time, its appreciated

[i.Annie]

So did you need to unlock or no?

If not, then a plain shift+restore would work. I would recommend jailbreaking with Greenpois0n, redsn0w is tethered on 4.2.1.

I am not sure if 4.2.1 is still being signed, so you might need SHSHs to restore to 4.2.1. So you'll have to test that out...

[Neil001]

Sorry, iTunes is no longer signing 4.2.1, 4.3 is out!! Use tu and check save my shsh and see if you have 4.2.1. Now do not go above 4.0.1 because you will update your bb and lose your unlock. If youdo have 4.2.1shsh saved then use snowbreeze or pwnage tool to create custom firmware to jailbreak and preserve you bb for unlock. Hope this helps