Superuser or Bookings Admin - Full access is required to cancel an appointment.
From the Account:
Click Org Tools > Accounts in the left navigation menu.
Locate and click the desired account.
Click the Bookings tab.
Locate the appointment to cancel and, under Actions, click the x icon.
Click Cancel Appointment to confirm.
From the Booking:
Click Bookings > Bookings Admin in the left navigation menu.
Locate the desired booking and click the gear icon.
Click the Appointments tab.
Locate the appointment to cancel and, under Actions, click the x icon.
Click Cancel Appointment to confirm.