1.
Download the firmware
2.
Download Odin
3. Open Odin
4. Extract the firmware's zip. You should have a .tar file and .dll file
5. Shut down phone then go into Download Mode (press and hold Home + Power + Volume Down)
6. Connect phone, Odin should say Added! (if not you should install drivers)
7. Add the firmware file to AP / PDA
8.
Auto Reboot and
F.Reset time should be
checked.
Re-partition is NOT ticked
9. Click start and wait about 9-10 minutes. Don't f*ck with cable wait until Odin says PASSED (green)
EDIT: After install, you might have some FCs. For me always do wipes from recovery menu.