Hello, I've noticed that PNGtube remix is using up a lot of my RAM (between 1-4GB). Is this normal? Is there any way to reduce the amount of RAM being used? Or is a RAM upgrade simply necessary for me to run this program while gaming (I only have 16GB)

depends, does your model have a lot of parts? and how big are textures used?
next update will have few things to somewhat counter that, but it may take a while till next release