Steady the black metal hub it plugs into with one hand and withdraw the plastic tube with the other. It's quite easy as long as you pull in the direction of the tube's long axis - don't apply any sideways or lifting force. You need to take it off now and then to clean the velvet and check its condition.
Of course, I DID misunderstand the title of your post when I first saw it and looked out of sheer curiosity!
Chris