To modify the size or shape of rooms that are already drawn we will edit the wall which encloses the room. There are various methods to do so depending on the walls relation other elements in the model. The behavior you'll observe is walls trying to always maintain the closed geometry required for the simulation to succeed.
Wall attached to Endpoints
One common configuration is a wall that is connected to other inline walls by their endpoints. When moving these walls, the connected walls will also shift as the tool works to keep all rooms completely enclosed. In order to modify walls in this configuration without impacted other walls follow these steps.
Draw a new wall in the location required to adjust the size or shape of the room.
Delete the previous wall that was in the old location.
Note that drawing the new wall first will retain the inputs into the rooms such as Name, Number, and Room Template.
Wall attached to Lines
Another configuration is a wall that is attached to lines on either side. For these walls they can be directly moved without impacted any other walls. To keep elements square while moving the wall ensure that the Line snap is turned on, this will keep the endpoints of the wall being moved inline with the existing lines. Editing these walls is easy following these steps.
Confirm that Endpoint and Line snap is toggled on.
Select the wall and move in the desired direction, keeping it square. Release when the rooms are at the required size and shape.