That PC actually counts with an I5 - 3470 CPU if im not wrong.
Assuming you have not mod anything on the CPU and it has the components of any other Optiplex 3010. Most of the Graphics cards this days actually bottleneck with that CPU.
The best you can aim right now its a GTX 1050TI but since i dont actually know your Budget i cant suggest you more options than that.
Also, to clarify: GPUs effectiveness on games are not entirely dependant on the Capacity VRAM has (in your case, yours has 1600mb).
It much depends on the Clock speeds it has, so i would say faster clocks Over Vram capaticy.
As i said before, stick to the Gtx 1050Ti and you will be more than fine.
Cheers!