At the same hotsprings you're going to and saving your corruptions, instead of interacting with that save tile open up your inventory and go into the transformation/curses tab. From there, you can click/press on the various transformations you currently have and as long as you have enough crystals, you can remove them until you don't have any remaining and are once again a basic/pure human.
I really don't think I or anyone else can get more specific outside of using pictures, and even then, this isn't hard to understand.