It’s usually the error with Apple servers that is responsible for over-the-air update of i OS devices.
When you transfer music or sync, i Tunes preparing to update takes forever. Note: If you are looking for other program to add your favorite music to i Phone, i Pad and i Pod, i Care Fone (previously i Phone Care Pro) would be a good alternative to i Tunes.
If the i OS 10 update is stuck at “Update requested…” for a long time, perform a hard reset on your i Phone by holding down the Power and Home buttons together until you see the Apple logo on your screen.
Once restarted, you can go back to the software update page and retry downloading i OS 10.
Unfortunately, if you’ve got an i Phone 4S, i Pad 3, i Pad 2 or i Pad Mini 1, you’re fresh out of luck.