How can I remove the cylinder from a Bernzomatic QuickFire propane torch?
This torch was discontinued, and finding replacement cylinders will be a chore. I read that the company did have an exchange program at one time, but that was several years ago so that may no longer be an option. You could try calling the Bernzomatic customer service line to see if they still will allow you to return it for credit towards a replacement torch.

The canister may be seized onto the torch, and I would not try to use force to remove it. The contents are under pressure, and may cause an explosion if excessive force is applied. My advice would be to light it and burn off all of the gas in the cylinder, and then safely dispose of it. They sell other torches just like this that accept full size cylinders that have all of the same features. I have had mine for many years and never had any issues.