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.
Samsung Galaxy Precedent (rooted, AreaRom 3.4 , sd-ext w/ 3.65GB internal space)
Kindle Fire (1st Gen, rooted, AOKP JB 4.1, Nova Launcher)
Samsung Galaxy SIII 4G LTE (rooted, Carbon ROM)