1) Open the booking that you want to cancel.
2) Click on 'Cancel Booking' near the top of the booking window.
3) Click on 'Ok'.
3) Click on the number next to 'amount'
4) Select bank or cash and Type in '0' and click on 'Refund'
4) Click on 'Accommodation' at the top of the booking window
(This to go back to the Accommodation view :)