There is an alternate solution if you have taken backup in your computer via itunes before upgrading to i.o.s7.
After upgrade you will be able to use only itunes 11.1 or above. Connect your iphone and open itunes.Click iphone menu. New window will open in which we have the option "reset iphone". Click and allow your phone to reset back up settings. After reset your iphone will get restart automatically.and the settings including the APN setting will be restored.
Note:- IOS will be remaining on ios7 itself.
Same will be applicable for IPAD too.
Regards,
Srijith