The Athlon X2 is not the best CPU for gaming, but it's adequate for most non demanding games.
The HD 5450 is actually your weakest link. You can play games with low resolution and low graphics quality with it. Therefore, that should be the 1st thing you upgrade. A Radeon HD 6670 should give you adequate performance to run most games at medium graphics quality up to a resolution of 1920x1200. The lower the resolution the better the performance though.