How to update SuperSu binary

Good evening guys,


I have a problem in my OPPO R831K, I can't update supersu binaries, I have search many times but all FAILED! I start the recovery mode but it always stated " Update failed" My phone is unroot but I want to root it again. So please help me n my situation, I know there is more benefits when your phone is rooted so please help me
Details of my Phone:
Brand: OPPO
Model Number: R831K
OS: Color Os
Ram: 1GB