Office chairs can be reupholstered. To decide if your chair should be reupholstered, carefully examine the overall construction of the chair. If the chair is cheaply made and the basic structure of the chair is plastic, then it may be more cost effective to simply replace the chair. If the chair is better made and has an underlying metal or wood base, then it may be a candidate for new upholstery. Removing the chair back is not complicated.
Remove the arms of the chair if the chair back is attached to arms in a removable way. For office chairs with plastic arms, you will see a plastic plug that looks like a flat circle. Pry up the plug with a screwdriver. This will expose a screw head. Unscrew the screws, using a screwdriver.
Unscrew plastic chair backs that are attached with a simple screw attachment. Many chair backs are mounted using an expanding barb-type fitting that slides into a post-type area in the inside plastic back. By pressing your fingers into the foam, you should be able to locate these. You may be able to squeeze the barbs together through the foam and release them. For better access, open the fabric seams with a seam ripper and peel up the foam.
Unscrew the barbed fittings from the plastic inside back after you have exposed and released them.
Rip the seams on office chair backs that appear fabric-backed. This will allow you to remove the fabric in a whole piece in case you want to use it again. Often there is an underlying chair back support structure that screws together. Simply unscrew this if you are trying to remove the back completely.
Speciality chairs often have additional features such as lumbar support or back adjustment screws. Contact the manufacturer of these types of chairs for tips on how to take your particular chair apart.