Can someone help? Thinking of upgrading something in my PC, but not sure which I should do! I'll list what I have in the text

I have problems with some games like GTA V, The Division Beta, more so open world games and I believe it's my graphics card but I'm not the most knowledgeable when it comes to this stuff. When I play those games they have to be low settings and you can tell it's not very smooth fps wise.

Intel Core i5-4670K 3.4GHz Quad-Core Processor

ASRock Fatal1ty Z87 Killer ATX LGA1150 Motherboard

Kingston HyperX Fury Black 8GB (2 x 4GB) DDR3-1866 Memory

Asus Radeon R9 280 3GB DirectCU II Video Card

PNY XLR8 240GB 2.5" Solid State Drive

Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive

EDITED..