Tone knobs are a major part of a guitar's appearance, and some players simply prefer one kind over the other. Even if the guitar sounds great and plays like a dream, they won't be happy until it looks just so. Luckily, changing the knobs is an alteration that is quick, inexpensive, easy and risk-free.
Find the tone knob or knobs on your guitar. Different guitars have their tone knobs in different places. Some guitars have one tone knob that is clearly marked as such. Some guitars have two that are not marked at all. A Fender Stratocaster has three knobs; one for volume (closest to the strings) and the other two for tone. A Gibson Les Paul Studio has four knobs, and the tone knobs are located nearest the bottom of the guitar.
Turn the stock knobs down to "0" so that you can calibrate the replacement knobs.
Remove the stock knobs: The knobs should come off with some gentle but firm pulling. Should you use a tool such as a pliers or a wrench, be careful not to scratch the guitar or strip the plastic ridging from the knobs you're removing (you might want them again someday.)
Apply the new knobs: The knobs should have a hole on the bottom and in the center. Turn the knob in your hand until its lowest setting is facing you, then line up the hole with the peg on your guitar. The knob should snap on easily. Now plug in your guitar and turn the tone knobs clockwise, then counterclockwise, to ensure that you have applied them correctly. At the farthest clockwise setting (10) the tone of the guitar should be trebly and sharp; at the lowest (0) the tone should be bassy and dull.