This tutorial shows how to move a reservation to a new room type without changing the price. This only applies to direct reservations created within the Cloudbeds PMS (Phone, Email, Walk-in, etc) and Cloudbeds Booking Engine.
For reservations coming from an OTA (Online Travel Agency such as Booking.com, Expedia, Airbnb, etc), you must change the room type on the OTA's extranet or ask the guest to modify their reservation. This way the reservation will be updated on both the OTA and Cloudbeds PMS. More information: Modifying Reservation from a Channel (applicable for all channels)