Answering my own question in case someone else needs to know how - the awesome folks at B&W answered me in an hour or so ...
"At the back of the speaker, you'll see the draw bar fixing in the middle (Large slotted screw head between speaker binding posts). Unscrew the draw bar fixing while holding the midrange at the front of the speaker. Once the draw bar fixing is unscrewed, you can pull the midrange driver from the front and out of the cabinet."
"At the back of the speaker, you'll see the draw bar fixing in the middle (Large slotted screw head between speaker binding posts). Unscrew the draw bar fixing while holding the midrange at the front of the speaker. Once the draw bar fixing is unscrewed, you can pull the midrange driver from the front and out of the cabinet."