1. Pull off the boot by pushing the rim to the right and lifting up.
2. Lift up the inner boot. (difficult to describe, but you'll understand when you see it).
3. Push down on a spring-loaded plastic collar. This exposes a metal pin.
4. Remove that pin and the **** and boot are disconnected.

When reassembling, make sure the plastic spring-loaded collar completely encloses the pin. otherwise the pin can (and will) work it's way out. This could make accessing reverse when you're downtown Chicago somewhat startling when the whole shebang comes off in your hand, and cab drivers are giving you the finger and the doorman is telling you to move that car or they'll call the cops.

Ask me how I know that.