Galaxy S5 Update Failed

My friend thought it would be cool to root my phone. I'll admit that I shouldn't of let him do it, I used apps to switch the status back to official and everything. Yet I cannot get OTA updates to go past 33% without it saying "Update Failed!" And my KNOX counter hasn't been moved to 0x1 so it tells me my warranty is still valid. What can I do to update? I really want to keep my phone up to date because i'm on the AT&T Next plan and i'm quite a loyal customer. I just want help for this.