If possible, upgrade the processor to an Intel Core I5-45xx or I5-46xx series processor. You will probably need to talk with the manufacturer to see if that upgrade is possible. Next, I would replace the RAM you have with at least 8GB of DDR3-1333 or DDR3-1600 RAM. Then I would change out the power supply with a quality 450w to 650w power supply. I would look towards Antec or Seasonic as preferred manufacturers. Finally, I'd look at swapping out the graphics card with a GTX960/GTX1060 (if and when available).
-Wolf sends