Normally, putting things together is a much more difficult task than taking things apart, and it's probably because we don't care about things as much when we're dismantling them as when we're following directions to put them together. Office chairs are no exception to the rule of easy disassembling. If you turn the office chair over and work from top to bottom (in this case, the top would be the wheels), you'll have it in pieces in no time.
Turn the chair over so that the base is facing upward, and check to see if the back rest is assembled with the base assembly, or if it's connected to the seat by the arm rests. If it's assembled with the base, the back rest will share screws with the base assembly (perform Step 4 to take it apart). If it's attached to the seat by the arm rests, you'll have to remove the arm rests to take apart the seat and the arm rest (perform Steps 5 and 6).
Pull the casters out of the base. This will require some force, but if you pull hard enough, the casters will come out.
Pull the base off the telescopic base height adjuster (the leg of the chair). Again, this may require some force, depending on your chair, but it will come off.
Remove the screws that the base assembly shares with the back rest and the back rest will come off. Remove the other base assembly screws to take the base assembly off the seat. Move on to Step 6.
Remove the plastic caps on the sides of the arm rests. The caps can be pried off with a flathead screwdriver or with your fingernails. Once the caps are off, you can see the screws that hold the arm rests to the seat and the back rest.
Take out the screws that secure the arm rests to the seat to disassemble the seat. Now the chair is completely taken apart.
Turn the chair over and pull the casters out of the base.
Pull the base off the telescopic base height adjuster.
Take out the screws that secure the back rest to the base assembly.
Pull the back rest out of the base assembly and then take the cushion off the back rest.
Take the last screws out of the base assembly and the seat will come off. Now the chair is disassembled.
If you plan on reassembling the chair at a later time, try not to strip the screws.
The base assembly is made of metal and it may have sharp edges on which you can cut yourself while twisting the screws, so be careful when you're disassembling it. You may even want to wear gloves to protect your fingers.