I have not had to Factory Reset my Z Force yet, through numerous OS Updates and system version updates. But when I have had issues in the past, with other phones, I have:
Turn Off the automatic "Back up my... " option in Settings.
Back up all personal data and Factory Reset.
Download & install the new update.
Factory Reset again if you feel it's necessary. Doesn't hurt at this point.
Start setting the phone up again as new. This is where Turing off the Automatic Backup My Data ones in useful....it let's you setup your phone fresh & clean, no auto download of the same apps & Settings you had before. Slowly start downloading apps and updating Settings, etc.