Photoshop uses as much memory as your images and presets take, that's it.
Unload presets you aren't using, and use smaller images if you want to use less memory.
I see, thanks for the reply.
Do you know of Photoshop also creates something like temporary files while I'm running the program and how to remove/limit them?
Yes, Photoshop creates scratch files as backingstore for the images you are editing, and some types of presets that use image data.
You remove them by exiting Photoshop.
You can limit them by limiting the presets you load and the images you edit.
You are confusing available hard drive space with memory (RAM).
The ideal situation is to have a physically separate, dedicated HD exclusively for Photoshop scratch.
The rule of thumb I follow to figure out scratch space says to figure on 50 to 100 times the size of your largest file ever multiplied by the number of files you have open. I have seen the scratch file exceed 800 GB once, an admittedly rare occurrence, but it often exceeds 200 GB when stitching large panoramas and the like.
As an example—and stressing that I'm aware that others have even more scratch space than I do—I keep two dedicated, physically separate hard drives as my primary and secondary Photoshop scratch disks and a lot of GB free on my boot drive for the OS. I also have 16 GB of RAM installed.
Additionally, if you only have a single HD, i.e. your boot drive, you'd need it to be large enough to accommodate both the swap files of the OS as well as Photoshop's scratch.
The question should be the other way around:
How do I provide Photoshop with enough memory (RAM) and with enough contiguous available HD space so that it can work efficiently?