1.Google iReb, click on first link then download
2.Go here http://www.iphoneheat.com/2010/09/download-ios-4-1-firmware-for-iphone-and-ipod-touch/ download what you need
3.Open iReb follow instructions
4.After step 3 your iPhone now is in DFU mode
5.Open iTunes it will say you have to restore, Shift+Click restore then select the firmware you downloaded in step 2
6.Let it Restore, then your done.