Default [Q] Galaxy note 2 question

Hello there I have a galaxy note 2 that is a t-mobile but unlocked and being used through att and rooted as well and I down loaded an app and it is I would say partially bricked I can get it to the Odin mode. I am not a computer guy and just traded my galaxy S3 and just found out it is rooted what do I do to g it back to normal and also is there a way that I can unroot it but keep it unlocked so I can use the tmoblie phone with att every time I try to down load Odin 3 it does some weird stuff on y computer and also can I down load the proper sites on my home Mac computer please help I need my phone thank you very much