hmm I see, I would say sell the HD7450, get a GTX 650Ti (boost) and get another stick of RAM (has to be clocked the same, and timings have to be same, just get another of the same stick to be safe) if you're in single channel, if it's dual channel I would suggest getting a new set of RAM, the best/fastest you can get that's compatible with your particular motherboard and CPU
there's not much you can upgrade besides these 2 components, to get a worthy upgrade on your CPU you'll need a new motherboard, and better Athlon X4's are not much better than yours as it is