How can I replace the gas cylinder in my new swivel chair?

Osteoporosis and multiple fractures to my spine have reduced my waist-upwards height by about 4", making it difficult for me to find any chair high enough to sit comfortably in at a desk or table. The draughtsman's swivel chair I have just assembled is unfortunately too high, so I would like to remove the gas cylinder without doing the slightest damage and replace it with one not intended for a draughtsman's chair - i.e. a lower one.

A helper put in the original gas cylinder so I did not get the chance to examine it with a view to seeing what I might be up against if I needed to replace it. I'm finding it difficult to obtain a replacement gas cylinder, but think I will eventually get one to do the job. Will it just be a matter of hammering the original cylinder out from the base and slotting a new one into its place?

The chair's packaging had no information with it (as to provenance) but the following appeared on the outside of the carton: SA 33 BE; SKU; 274498; and GGI.

Whoever has any ideas, thank you! Your advice will be much appreciated.