You always want at least 8gb of ram for intensive gaming. Preferably dual channel ram aswell. Your GPU will not play a significant factor on your ram, that's why gpus now have vram, your has 2gb of vram which is good for medium to high settings at 720, for 1080p and above your going to need more vram on your card, 3gb_4gb. The vram is where your gpu stores the shades and mappings that it can reuse to render games.
I suggest a dual channel 2x4gb ram set. That will do you fantastically. And in the future you should either buy a copy of your card to crossfire/sli for a total of 4gb vram, or just buy a new card 3-4gb.
For example grand theft auto 5 uses up to 4gb of vram, fallout 4 uses up to 4gb of vram. That is max settings of course.
Your memory modules do not play a real key role in the gpu rendering of games, at most it will result in a 1%-3% increase in fps if you actually needed the ram in the first place.
The gpu mostly communicates with the cpu, so the better your cpu the faster it can handle the point float performance and the rendering of vertices for the gpu.
To improve graphics you will want to look at first a gpu with a good amount of vram, 8gb is overkill on vram, you want 8gb of memory, and a cpu that will be able to keep up with the gpu to avoid bottlenecks.
Hope this helps and explains in more detail.