I agree with Nerd here, upgrading 1 part will be bottle necked by the other, considering you have a first I5 gen CPU I'd recommend a new system really. While the CPU is still decent, it will hinder you alot on new titles (from like 2013+). I'd do lots of research if I was you to find the best hardware for what you want in-particular, save up around 500- 750 and get a decent CPU (Ryzen is probably a better deal for all round performance, especially as you can overclock all the CPU's in the line up assuming you get the right motherboard.) and a good mid range GPU (rx 570/580 or gtx 1060/1070) and atleast 8GB if not 16GB of RAM.