I. Before You Begin
1. Yes, I did use an iPhone for this procedure, but it will also work on an iPad or iPod Touch as well (just choose the right firmware for your specific device when prompted in the procedure).
2. You must have the latest version of iTunes installed. If you don’t, download it from Apple here.
II. Download the Stock Firmware
1. Head here and select your device’s firmware in the drop down box under iPhone and select Download (remember to select the firmware for your specific iPhone model, if you need help figuring out which is yours, see this here).
III. Put Your Device into DFU Mode
1. With the device plugged in to the computer via USB, turn it off.
2. Hold down Power and the Home button at the same time until you see the screen go from the Apple logo to black (approx. 10 seconds) then let go of the Power button but continue to hold the Home button until iTunes pops up a dialog box saying it has discovered an iPhone in recovery mode.
IV. Flash the Stock Firmware
1. In iTunes, select your iPhone from the sidebar on the left.
2. Now, hold Option on your keyboard (or Shift for Windows) and click on Restore.
3. When the selector appears, choose the firmware file you downloaded earlier and click OK.4. When the device restarts and is done, select the backup you made of the device before you upgraded to iOS 7 when prompted to restore your apps, contacts, etc. (if you made a backup before updating to iOS 7, of course).