It is possible to replace caster wheels on office chairs. Websites such as eHow.com or FamilyHandman.com provide a list of needed tools and step-by-step instructions to accomplish this repair.
If a caster wheel on an office chair is not working, first check to see if there is any dirt or debris that may have created the problem. Sometimes it is possible to fix the problem merely by cleaning the wheel.
If you must replace the wheel, determine the appropriate size caster wheel. Also, when you purchase a new wheel, make sure to buy a wheel appropriate for the surface the chair sits on. Retailers such as Office Depot and Amazon.com sell caster wheels.