Can you verify motherboard is an MSI H81M-E33?
Yes differing specs for this motherboard if it is E33
To buy 32GB (16x2) modules is around 3 hundred dollars.
Are you prepared to spend 300+ dollars on your system just for memory?
If this board had 4 memory slots then it would be about 2 hundred dollars for the 32GB.
This is a typical boutique computer. They flash it as a performance computer with a decent CPU yet use a motherboard that has limited upgrade path with a 500 watt power supply and charge a premium. Unfortunate because it does limit your upgrade path.
As you learn and would like more performance from your computers, always look for better motherboards with 4 memory slots usually. Even if you don't use all 4 slots, sometimes slots go bad or if you upgrade your CPU cooler you need to move the memory to different slots, etc.
Unless, you tend to sell your systems more often instead of upgrading.
I still tend to get full ATX motherboards for myself even though I don't always use the slots. Habit from all the years of buying computers and adding on things.
Another upgrade path would be to upgrade to 16GB memory and put a SSD (solid state drive) as your boot drive instead of that mechanical hard drive. It will make your system pop.
Any future upgrades would be the graphics cards. I assume this was the reason for the power supply upgrade unless it was due to failure.
Best of luck.