This is an "it depends" answer. It depends on the type of gearshift knob and its installation. If your vehicle is equipped with a manual shift and the shift lever is little more than a steel rod sticking up from the console, then it is easy to replace.
To replace it, simply do this:
1. Set the parking brake
2. Take the car out of gear
3. Center the gearshift
4. Place a piece of cloth around the gearshift knob to prevent damage
5. Place a ViceGrip (R) or pair of pliers around the cloth on the gearshift knob and gently begin turning the knob to the left
6. Spin the knob off the shaft
Remember, though, this works only if the gearshift knob does not have another function combined. For example, you might find a reverse gear actuator on the top of the gearshift knob or you might find a reverse actuator button on the front face of the gearshift knob. This type of combined function gearshift knob is usually found on automatic transmissions.
If you want to remove the gearshift knob from this type of shift, see the service manual and obtain the tools you will need as this type of gearshift knob is much more complex to remove and involves many different systems that have to be addressed before the knob will come off.
It is better to leave this type of fix to trained technicians.
If you need further information or if you would like to see information on automotive safety please visit this site: Safecar infoCar safety Insurance Magazine