I'd upgrade the ram, try to get at least 8GB in your rig before you do anything else. After that you can upgrade your Graphic Unit to a NVIDIA GeForce 980, but don't buy one with a higher number like a 1080 since you will need to upgrade your cpu at the same time. I believe the higher end graphic cards like a GTX 1080 can't use their full potential power unless the CPU is just as powerful so purchasing one at this stage would be of no use to you unless you upgrade the CPU to an i7 for example, as well.