THIS IS FOR THE G930A AND WILL WIPE ALL USER DATA. If you have a different model number please state it so I can post the right firmware.
If you can't get it to update you can do it manually using Odin. Only do this if you can't find a way to do it on its own.
Here is the Firmware: https://androidfilehost.com/?fid=673791459329073619
Here is Odin: https://androidfilehost.com/?fid=24591023225177749
To flash get your phone into download phone by turning it off then holding Volume down, Home, and Power at the same time. When prompted hit volume up.
Now plug in the phone to your PC and open Odin.
You should see something under the ID:COM like COM##
Extract the Firmware
Click CSC and the Corresponding file (Should start with CSC)
Click CP and the Corresponding file (Should start with CP)
Click BL and the Corresponding file (Should start with BL)
Click AP and the Corresponding file (Should start with AP) {This verification might take a while, it is a big file}
After that click start and it will start flashing. (This will take a while, DO NOT UNPLUG OR TRY TO STOP IT)
The phone will reboot and Boot to Android, It might take a while just let it do its thing.
When it boots just go through the setup and you should be good! If you have any problems or questions just ask!