First you have to plug the "iPad " to the computer and open the " iTunes".
Now put your iPad device into "DFU" mode so that you will restore the device .
For putting the device into DFU mode by just follow the steps:
Turn "OFF" your "iPad" and "HOLD" down power button for 3 sec.
After enter into "DFU" mode your "iPad" screen goes blank and get pop up message in iTunes apps “Device in Recovery Mode".
After all these your iPad device will start to restore back to the i OS firmware.
This process will take latest 10 minute for processing so never disturb or do any thing with device.