IOS – Is it currently possible to upgrade iPhone 4 from iOS 5 to iOS 6

As mentioned in the firmware signing status for iPhone 4, only iOS versions from 7 and up are being signed by Apple.

In order to use redsn0w to do a downgrade, you need the SHSH blobs saved for the specific version that you wish to downgrade to. In this case, it seems like they were never saved while the phone was on iOS 6.1.2. So you cannot create/retrieve them.

1. Restore the device with iTunes (connect the device and click Restore in iTunes).
2. Once the device is restored, set up the device using an iTunes backup and select the iTunes backup that you made before you restored the device.
3. If you want the device jailbroken, jailbreak the device using evasi0n 7.