You didn't say what graphics card you have.. 2GB is extremely vague. However, a lot of modern games usually require 4 GB+ of VRAM. Also, most games recommend at least 8 GB of RAM, and a few require 16.
In short, your PC is most likely not good for gaming. You have an outdated CPU, too little RAM for the majority of modern games, an unknown graphics card which may or may not be good, etc.
Adding more RAM won't help too much. In gaming, the most important part is the graphics card (which we don't know what it is), and the CPU (outdated).