If all your rooms are occupied and you want to swap reservations on Bed View, you can easily do that using Unallocate and Allocate options. Please see the example below.
As you can see in the image above the is no availability in Double Rooms and I don't have any additional room which I could use to switch reservations. I want to move:
Reservation 1 and Reservation 2 to Room 4
Reservation 3 to Room 3
Unallocate reservations from one room.
I unallocate Reservation 3 because it occupies the whole room for the dates I want to change.
The reservation will appear in Unallocated Bookings section. See Where to find unallocated bookings.
Using Move Reservation option from the menu, move Reservation 1 and Reservation 2 to Room 4:
Allocate Reservation 3 to Room 3 using Auto - Allocate option.