How to root at&t galaxy note 4 on Android 6.0.1 ?

I upgrade my at&t note 4 on Android 6.0.1. I want to know if his bootloader is locked? Can I use Kingroot to root it? Can I downgrade it on 5.1.1 with Odin? Marshmallow working fine on my att note4 ,but I need root on it. Thanks you for your help.