When you take out the centre spinning section you should be able to push down the bit with the 3 small brushes on it. The centre fixing will not go down with the rest, but if you put a flathead screwdriver underneath it you can wedge it off and this dismantles the whole mechanism.
Be carefull though, this whole mechanism is sprung so hold it tightly when taking it apart. Also, the zip brush will not work properly and won't vibrate at all if not reassembled EXACTLY the way it was before it was dismantled.
Hope that helps.