Need help rooting i337

Hello,

First of all I'll begin by saying that I am a bit lost with all the terminology of root, ROM etc.

I have the sgh-i337 (version: 4.4.2), I337UCUFNB1 (bulid number: KOT49.HI337UCUFNB1)
I want to upgrade it to Lolipop 5.1

I searched for guides in the forum, but I don't know which one is right for me.

I would be very happy if you guys can give me a simple explanation and a guide to how to do it.

Thank you.