I have a 3GS with 3.1.3 and the Spirit jailbreak. I want to upgrade to iOS 4, so I guess I need to uninstall Spirit. My SHSHs are on file with Cydia.

The problem is that the Mac I sync with was stolen. I can download iTunes again to another Mac, but I think the current version (9.2) doesn't work with Spirit.

What should I do?