According to the specs you can easily upgrade to 32gb using 2x16gb:
https://www.acer.com/ac/en/HK/content/model/DT.B8ACF.001
But as far as the gpu upgrade, I would NOT upgrade in this case/power supply. And I can tell you why.
The system design you have dates back to much earlier when it was a Gateway branded product. The case is actually a refashioned sx2803:
https://www.gateway.com/gw/en/US/content/sx-series/sx-series
Now, the sx2803 was an lga775 system, but just used a flex-atx style motherboard with a small flex power supply. The good thing is that these are standard parts, so the motherboard can be transplanted to a larger case, you can use a larger power supply, etc. I know this because I have an sx2803.
Your Acer looks like it can do the same things--move the motherboard to a new case, and have a larger power supply in that case.
The power supply in the sx2803 was cheap and failed after I powered the system on for a week and then put it in storage for a few years. It wouldn't power back on again when unboxed. It is also not powerful and should not be used with more power hungry gpus. This is probably the same power supply you have installed in your Acer. I would not use a new gpu with this power supply, especially if it needs any power connectors. The other problem with a gpu upgrade in these systems is the case as there is little room for a gpu in it, limiting what gpu you can add.
Because almost any standard case will fit the motherboard, I would look for one cheap locally and transplant the motherboard and system to it and then look for a new, quality power supply. Once you have the power supply, you can look to upgrade the gpu and ram, etc. Eventually you could even upgrade the motherboard and move to a newer processor while keeping everything else intact. This is the benefit of a modular system that is not proprietary.
Hope this helps.