Enter your iPhone into DFU Mode /Recovery Mode to try again
- Connect device to your computer and launch iTunes.
- Turn the device off.
- Hold and press the power and home buttons together until the Recovery Screen appears. Then update your iPhone with iTunes.
- Connect the device to the computer and launch iTunes.
- Press and hold the power and home buttons together for 10 seconds.
- After, release the power button and just hold the home button for 5 more seconds. The screen will go completely black. Then update iPhone with iTunes.