You can cancel or change your booking via their self-service tool 'My Booking.com’ which you can access here.  Please, remember to check the hotel’s cancellation policy before making any changes to your booking. Non-refundable rooms and other special deals can have a different cancellation policy. Room specific cancellation information is included beside the room type under the ‘Conditions’ column http://support.lonelyplanet.com/hc/en-us/articles/218157847-How-do-I-view-cancel-or-change-a-booking-I-made-through-Booking-com-