Whether they are broken or just need upgrading, volume and tone knobs can require replacement. It is a simple procedure, but takes some care to avoid damaging the knobs or the guitar's finish.
This type of knob will have a hexagonal screw somewhere on the side. Locate the screw.
Insert the hex wrench (1mm and 1.5mm are the most common sizes) and turn the screw counterclockwise.
Pull off the knob.
Hidden Screw Knob
These knobs have a seam around the top. Pry the top off gently with your fingernail to expose the screw.
Turn the screw counterclockwise with a screwdriver.
Once the screw is out pull the knob straight off.
These knobs have neither seams nor hex screws. Take thin piece of cloth and wrap it underneath the knob.
Twist the cloth to get a good hold on the knob.
With gentle but firm force, pull the knob straight off.