you have to download the .ipsw firmware you want to install. then sync with iTunes, then hold the SHIFT key and press the restore button.
It will ask you what firmware you want to restore to, click the one you downloaded.
If your on a mac. I can't help you sorry
Try this link for your firmware download
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+rep if i helped
---------- Post added at 05:24 AM ---------- Previous post was at 05:18 AM ----------
also i got a 3g ipod touch but i jailbroke it so it now says 2g ipod touch. it gives me a 3002 error when i try and restore using a 2nd gen ipsw and when i try it on a ipsw for 3rd gen it says non compatible. soo how do i donwgrade it?
just grabbing your attention