Help with upgrading?

Hey guys

Fairly new to building PC's but been gaming a few years.

Basically I want to upgrade my graphics chip, I was thinking a GTX960 would be good for my needs (unless you guys have any better suggestions) however when looking it up I see there are many variants of the card, which one should I get? I assume an AMD one but I have a gigabyte motherboard so do I get the gigabyte one for optimum use?

Sorry if it's a dumb question but my friend built the PC and I bought it off him a few years ago, we all need to start somewhere!

Thanks in advance!

System specs Graphics Chipset AMD Radeon HD 7800 Series Memory Size 2048 MB Core Clock 900 MHz Windows Version Windows 7 (Service Pack 1) System Memory 8 GB CPU Type Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz