It is not a difficult or expensive job. A local shop should be able to do it very easily or you could tackle it yourself, if you are inclined.
If you do it yourself, getting the right pot is important to good results. If your guitar has humbuckers, it almost certainlyhas a 500k ohm, audio taper pot as the volume control. If it uses only single coil pickups, rather than a mix, it likely has a 250k ohm, audio taper pot. If the top of the guitar is carved / arched like a Les Paul, you'll need along shaft pot, otherwise the standard type is the best choice.
A pot has 3 connections - top, wiper and bottom. Normally, when used as a volume, a signal is connected at the top, the bottom is connected to ground and the variable wiper int he middle is the output. As the pot is turned, the wiper moves, changing the resistances between signal and ground. Turned up, the wiper is near the signal connection, so there is low resistance to the signal going out on the wiper, but a high resistance to it getting drained off to ground. Turn down and the opposite is true.
Anyway, the steps are: open the access panel on the back of the guitar by removing some screws; do a quick visual inspection to see that there are no broken/loose wires and the pot value is correct (look for a printed 500kA on the back or side); Desolder the connections making a note, if needed about their position and orientation; pull off the volume knob (check for a set screw first, but many just push on); loosen the nut holding the pot in place being careful not to scratch the face of the guitar; extract the old pot; before installing the new pot heat a spot on it's case and flow a little pool of solder onto it, for grounding, as this is a high heat operation compared to the rest of the job and so, easier done on the outside. Finally, install the new pot, orient it, tighten it down resolder all connection. The last step is to replace the access panel and knob.
Roadie & Reviewer