In order to view/cancel your booking, click on the highlighted blue confirmation number.
Review your reservation details and if you wish to cancel your reservation within the cancellation period of your specific property, then and only then, will you be able to cancel the booking by clicking on the large green button reading "cancel this reservation".
If the large green button reading "cancel this reservation" does not appear then you are outside the cancellation policy of the property and you must call the property directly to cancel the reservation.