Remove all retainer screws fastening the outer encasement of your electronics device. It would be best if you are able to obtain a copy of the schematic diagram for your device, if possible, but it's not absolutely necessary. Pay close attention and be sure to remember how you take everything apart to aid in putting the equipment back together again. Remove all necessary case covers and dividers so the rear of the variable resistor may be accessed with your soldering iron.
Heat up your soldering iron to about 35-degrees F. Unroll a one-inch to two-inch portion of de-soldering wick and touch it to the solder connection on one of the wires that are connected to the rear of the variable resistor. Touch the tip of the soldering iron to the de-soldering wick and use the iron to press the wick down onto the solder joint, holding it in place until the old solder flows from the connection and into the de-soldering wick. Quickly remove the wick once the solder has all flowed off of the connection. Cut off the saturated portion of the wick and use new wick to de-solder each wire.
Use a jeweler's screwdriver to loosen any fastener screws that are recessed in the knob on the front panel of your equipment. Most potentiometer knobs are fastened down onto the adjustment post using a small set-screw. Loosen any such screw, or fastener clips, with the jeweler's screwdrivers and remove the knob.
Use a pair of pliers and remove the fastening nut from the threaded potentiometer neck. Hold the "pot" from behind to prevent it from falling when the nut is removed and then gently pull the old "pot" from the equipment.
Insert the new "pot" into the panel and screw down the fastener nut onto the threaded neck of the new one until slightly more than finger-tight. Replace the knob in reverse-order as you removed it.
Solder each wire onto the terminals of the new "pot" in the same order. Since wiring colors and sorting vary amongst all devices, be certain the wires are all soldered onto their respective terminals in the same way they were removed from the old "pot." Use rosin-core solder for this purpose. Replace the appliance covers and fasten down securely.