Just like when you sell a used device, make sure to factory reset it before sending it in. I haven't upgraded from the S5, but I imagine there is a place under backup and restore to NOT restore apps etc. I would suggest doing that. You could even go the extra mile and turn on reactivation lock. When it gets factory reset, only you would be able to unlock it to boot back up; ask me how I know? I locked myself out of my Gear S2 with the reactivation lock, mailed it in (under warranty) and they had to replace the motherboard for it to work again.