If only renovations were so easy! Once a room has been created, you cannot change either the size or the style. 

If you want to make a bigger room, or a room with a different layout, just click on 'Rooms' in the top left-hand of your screen when standing in any room. From there choose the 'My rooms tab' and hit 'Create a Room'.

Accidentally make a room too big or too small? You can delete any old extra rooms by heading to your room description page, then going to Edit>Basic Info>Delete room.