Just a quick question about the knobs on a guitar. Are they supposed to just pull off or is there something more you need to do to change them, it is on a Gibson Sg.

They just pull off, but they're a really tight fit.
Best get something to lever them off with.
Make sure you protect the body with something like card board, and ease the knobs off a little at a time making sure that they come off evenly

Make sure there not speed knobs they have a screw you have to untighten.