Restoring/Downgrading/Clearing iPhones

There's a few scenarios why you may want to do this:

• You want to clear out the iPhone as it has slowed down over the year(s)
• You want to sell your iPhone (or change owners) 
• You want to unjailbreak it to take it back to the Apple store

Generally speaking, you can do this by simply connecting your phone into iTunes and then clicking "Restore"; this will wipe your phone and install the latest iOS available... this, however, may not the solution if you want to keep your iPhone jailbroken or on an older iOS.

If you need to take your phone back to the Apple store, you will need to unjailbreak your phone and update to the latest version. From Apple's point of view, if you are not using the latest iOS, then you have not attempted everything to resolve the problem you wish to discuss. This obviously means you will have to re-jailbreak the iPhone post visiting the store... if a jailbreak is actually available for the latest iOS. 

Downgrading or Re-restoring your iPhone

• Re-restoring means, you want to remain on the same iOS version you currently have on the iPhone e.g.  iPhone currently on iOS 5.1.1 and restoring to a clean iOS 5.1.1. because iOS6 jailbreak is not available.
• Apple stopped signing iOS 5.1.1 in Sept 2012. This effectively means that the following process will not work if you want to remain on iOS 5.1.1. I've detailed the steps below as it will work if you are on the latest iOS release: 
• Download the IPSW file for your device: LINK
• Put your phone into DFU mode: Link to Instructions
• Connect your phone to the PC and load iTunes 
• Hold Shift + click Restore button  (Alt/Option + Restore on Mac)
• Point the file to the downloaded IPSW
• Note: for iPhone 4S, you will need to wait for Redsn0w to release an update of their software - skip to "cleaning your iPhone without re-restoring" below.
• To be able to downgrade or re-restore your iPhone 4 (or lower model), you will need to save your SHSH blobs and use Redsn0w to stitch it to the IPSW file.
• Note: Run Redsn0w on as Admin. (If on Win7, set Compatibility = WinXP SP3)
• Saving SHSH blobs: Link to instructions with Redsn0w  and with iFaith (download link)
• Stitching blobs to IPSW and downgrade/re-restoring: Link to instructions
• Another set of instructions for both processes from SiNfuL iPhone forums

Clearing your iPhone without re-restoring

• Why? All the processes above will not work because, Apple has stopped signing the iOS you want  AND you currently cannot use the SHSH blobs (e.g. iPhone 4S A5 device as at Oct 8th 2012)
  .
• Non jailbroken iPhones:
  On the iPhone click:  Settings > General > Reset > Erase All Contents and Settings.
  .
• Jailbroken iPhones:
• Removing all apps and accounts
• Sync the iPhone with an empty iTunes account/library
• Log out of iTunes store
• Manually delete any remaining data: Messages
• Run iCleaner to clear any random caches, etc. (see previous blog entry for details)
• Removing all Cydia Tweaks
• I have not tried this, so please backup and read all the instructions carefully prior to attempting anything. 
• Link to removing all Cydia Tweaks on ijailbreak