A:Answer Priorities in this rig to upgrade:
1. RAM: Upgrading the amount of RAM will provide major performance improvements as the computer will be able to multitask better
2. Motherboard: Upgrading the motherboard will allow for more upgrades down the road. Remember, make sure the CPU and motherboard are compatible (Example: The Ryzen 5 3600 is compatible with B450, X470, B550, and X570 motherboards)
3. Cooling/case: This system tends to overheat when put under major stress, but there aren't any spots in either the case or motherboard to put more fans without making it jank. In this case (pun intended), you'll have to get a new case to put the components in and a new motherboard with more fan headers. Along with this, it would almost never hurt to get a more powerful CPU cooler and more case fans.
The other components are fine the way they are unless you want maximum performance.