Use RedSn0w 0.9.15 beta 3. Use the Restore feature in Extras > Even More > Restore. Select the iOS IPSW that you want to restore to, and select Remote for blobs. When prompted to, put the device into DFU mode then Pwned DFU it when instructed.
Eject the SIM tray while the device is on, unplug it from your PC. Give it a minute for your device to say No Service. Put the SIM tray back in, let it recognize the SIM, then plug it into your PC.