You need to put the iPad/iPhone into DFU (Device Firmware Update) Mode in order to update the firmware.
To enter DFU Mode on an iPad, follow these steps:
- Launch iTunes.
- Plug the iPad into your computer.
- Hold down the Power button and the Home button at the same time, for 10 seconds.
- After 10 seconds, release the Power button but continue to hold the Home button for another 3 to 5 seconds.
- When in DFU mode, your iPad screen will stay completely black. If you see an Apple logo or anything other than a black screen, the iPad is not in DFU mode.
- iTunes will notify you that it has detected a device in recovery mode
- Once in DFU mode: in iTunes, shift-click (Windows) or option-click (OS X) on the “restore” button once iTunes tells you it has found an iPad in recovery mode.
- Select the firmware file you downloaded.