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Back up everything you want to keep manually.  Copy your pictures and media to your PC.  Use something like SMS Backup and Restore to back up your texts to email or some sort of.onlike storage.  If.you save that backup locally, you will need to copy that over to your PC as well.  Double check you have everything you want stored somewhere off of the device before factory resetting. 

Once you factory reset, do not use Smartswitch or Samsung to restore.any backups.  It is okay to allow Google to restore your contacts but not apps.  Set everything else up like it's a new device.  You should get a text from T-mobile saying your device does not have the correct settings for MMS and internet and that it will send those settings to your device.  Texting should then work properly through Samsung's and Google's texting apps.  You can restore the text backup through SMS Backup and Restore using their app after that point, if you want all of that restored.