In order to rearrange your rooms you need to move reservations to room numbers that are free. Sometimes you will need to move them to the holing area while you are rearranging your rooms. 
Right click on the reservation you would like to move, hover over "Quick move" and select the new room number or the holding area. 
Note: all the rooms that are above the line Other Rooms are the same room type as the reservation is in, everything under that line is a different room type.