Help with changing sizes and proportions of character morphs?

This may be hard for me to explain, so please bear with me.

I create playable morphs that come in all shapes and sizes. I do this in, what I assume, is the most standard way possible, and they function in the same was as any morph you can find in Free Models. Some of my characters are so big that I need to change the proportions of the rig(?) within it so that it can walk/jump normally.

I'm not asking for anyone to write any scripts for me, but I am curious if anyone knows of any tutorials, guides, or even existing free models that I can experiment with. I feel as though morphs are common enough on Roblox to have some sort of helpful guide for but I can't find anything at all.

My morphs aren't too complicated, and are mostly human-like. I mostly just need to alter the rig's leg, torso, head, and/or arm sizes without breaking it completely.