Originally Posted by nickdalzell
if it was done via a root custom ROM you can possibly search somewhere and find a stock ROM in 'nandroid' (that's backup) form. if it was done that way it should have a custom recovery in it, like TWRP or ClockworkMod. if it was done OTA, there may be no going back to GB, as i have read some who OTA upgraded now have entirely different bootloaders and it's a one way trip.
Sorry but I'm very new to android, could you explain in much simpler terms how I can find out if was a custom rom and how to then downgrade?