Tried 4 times to do the upgrade, Samsung advised my to try it in the Safe Mode, which I did still will not upgrade.
I would plug your phone into your computer, make sure you have it set on installer, not MTP and then run a software repair. Be prepared as it will wipe the phone.
This is for the S5, but it's the same steps on running the repair.
Repair Assistant Software Upgrade Assistant (Samsung) | Verizon Wireless
