need immediate help with Note 2 (Modified)?

I Just brought the note 2 off my mate, who originaly bought the note 2 from kogan. it was sold as an unlocked handset. when i attempted to update the phone today i was told that i can not update becasue i have a modified phone, will doing a hard reset fix the modified problem and revert my phone back to normal? will the phone stay unlocked, or if it gets locked to a carrier other than the one i have is their a way to unlock the phone so that i can still update, PLEASE HELP!!!!!!!!