>>357507183
Uhhhh
Decent edits require both blender and unity. You're going to have to learn 3d modelling. We can answer questions here; or you can check the pastebins for some starter resources.
 tl;dr, open booth in blender, perform edits, export to fbx, load in unity, configure in unity, upload to VRC. 
It's a lot to learn desu, so if you just wanna go straight from booth to unity to VRC that's fine too - you can get some texture editing done in GIMP and whatnot.