When you call, make it very clear that you want to modify the reservation and not cancel it. You might need to speak with a supervisor because some reservationists will want to cancel and re-book since that is the easiest way to change the party size. You do NOT want to cancel and re-book because in the brief time between canceling and re-booking someone else may snap up the reservation and then you would be without a reservation. If the castmember wants to do this ask for a supervisor or hang up and call again.