Ir you just want to upgrade, then I suggest an RX 460. It's a 2gb card, and I bet that 650 you have is a 1gb card. Right there it improves your gaming experience. Plus it's faster than the 650, so that helps too. If you can find some cheap, adding another 4gb system ram may help in some games.
The main to to know is this, at best, is a budget set up. Keep your expectations reasonable and you'll be satisfied. If you are wanting to play the newest games at 1080p and high settings and 60fps, it's not happening with this system.