So I updated my Iphone 3GS with the new iOS 6, but I'm not getting any service on my phone after I updated it. I did just replace my iphone with a new mother board, but it seemed to be working fine until I upgraded it. So I'm trying to downgrade my iphone back to iOS 5 and I went through a tutorial video by putting my phone in DFU mode. Every time I get to the step where you have to find the file of the firmware on itunes, I can't find it! Every tutorial is using a Mac, and I'm so confused trying to find the firmware on Windows. I've looked under itunes file and apple software update, and I even searched for firmware on my computer. Please help! I even tried finding a link online for the firmware, but everything is for a jailbreak? I could only find a downloadable link for the ios 4 and 3.
Added (1). I have Windows 7