So I have an iPhone 2g. I had the 3.0 software installed but wanted to go up to 3.1.3. due to a few programs requesting that I have 3.1 installed.
I started out the day thinking it would be quick and painless. There are a few sites out there that tell you how to do it but a lot of the info is convoluted and not explained well.
I made the mistake of restoring my phone to 3.1.3 using iTunes and then upon not finding the files necessary on my PC, trying to complete the unlock and jailbreak on my Mac. That is a big no no. Don’t do it.
I ended up having problems with the IPSW file. Apparently when you download the IPSW file to a PC, it automatically thinks the file is a .rar or .zip file. In turn, it wanted to be opened and uncompressed. You have to change the file extension. You will have to go into folder options and tell Windows to show file extensions for all files.
You can then change the extension of the IPSW file from .zip or .rar to .IPSW and that’s that.