The volume control potentiometer is usually a small, circular component with three legs. It's connected to the PCB and has a shaft that extends to the front panel of the control unit. Gently desolder the legs of the old potentiometer from the PCB. You may need to use a desoldering wick or a pump to remove excess solder. Once the old potentiometer is removed, take note of its orientation and position, as you'll need to replicate this when installing the new one.