Before you restore it, a few things to try:
After updating, reset is recommended: press and hold Home and Power button at the same time until the Apple logo appears.
Restart your device: turn it off, wait for a few minutes, turn it on again.
Turn off 3G (Cellular Data) in Settings. Then turn it on again.
Go to Settings - General - Reset and Reset Network Settings. Then set up 3G and Wi-Fi again.