Can somebody explain this:
http://imgur.com/a/xTCzl
Only 54% of ram used and 10 fps
Without seeing the rest of the processes you have running or what your graphics setup is not much help I can offer here. 280MB to run the application (if I read your screenshot correctly) isn't much so obviously something else is taking up that 54%
My question is why the game is not using more memory to keep the fps high because my computer still had a lot of free memory
That's not how computer programs work. They don't gobble up all available memory, they use what they need (and swap out to disk when they run out).
So you're saying that I'm going to need to buy more memory to keep the fps high
