Every room or group of rooms has an Accommodation Payment set for it. If you elect to move from a room with a higher Accommodation Payment to a room with a lower Accommodation Payment, then you will be asked to pay only the lower Accommodation Payment on transfer and, therefore will be refunded any amount paid in excess.
Alternatively, if you elect to move from a room with a lower Accommodation Payment to a room with a higher Accommodation Payment, you will then be asked to pay that higher Accommodation Payment.
You will have the choice of paying this additional amount either by RAD, DAP or a combination of the two.