If you want to go back, make sure you havea copy of the firmware file and take a copy of the database on the device. Then you can install the firmware and replace the database with the copy.
The upgrade should go OK without losing anything. But, I have never tried or heard of anyone making that big a jump in version. I know the upgrade will work after a factory reset, but that is starting from an empty device. If there is a problem, it will be because of the database can't be migrated properly.
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