You should have the RAM as two sticks in dual channel , which will improve performance so the first buy is another RAM stick identical to the one you have . Follow the mb manual on which slots to use to get dual channel
The next thing to upgrade is the graphics card , but this depends in part on the resolution of your monitor .
It also might be limited by your " generic psu" . Just because it ways 650 watts doesnt mean it can produce that current without exploding . Got any details on the unit you have ?