How to combine instrument soundfonts from many .sf2 files into one smaller new one

I hate this!!!!! I hate having to pester you guys with new questions, but ... try as I might, I can't seem to figure out how to open an existing orchestral soundfont in Polyphone, then open a new .sf2 file, then copy a particular instrument/preset??? from the existing file and paste it into the new one, then save the new file, so I can slowly create a custom .sf2 file containing only the instrument fonts I want. I can open an existing .sf2 file in Polyphone and see its instruments and/or presets, but when I click on any of them, the toolbox turns off. I can't click on a preset or an instrument to copy it. Also, I don't know how to have two files open at once in Polyphone, even if I could copy a preset from one place to another. I'm sure this is not complicated, but would someone please just outline the steps needed to do this? I really want to learn how to isolate instruments from a variety of soundfonts into a smaller, leaner custom one.

Sorry for the effort to reply but many thanks in advance.