About root... topic

Hello all...

I have a note 2 with stock firmware android 4.3, and unfortunately with knox, I did root, with chainfire auto root and does not work superSu!!!
It do not has root acces!!!
does anyone know what I need to do, please?

I would like to know if I can unroot and install stock firmware with android 4.1.2 I do not have any issue?

I will be waiting for your help, thanks