They both mean the same thing. Both phrases are about revenge. For example, if someone has hurt you, by hurting them back, you would be getting your own back or getting even. The only difference is in sport. In sport 'getting even' can mean a losing team scores to tie points with the other team, however 'getting your own back' in sport would usually refer to a player fouling against another who has previously caused foul play. I hope this helps.

Thank you Owen!

I have never heard "get your own back", although perhaps this is something said in England. An equivalent expression to "get even (with someone)" is "to get back at (someone)".