Replace a room with a bigger one?

[Papaschtroumpf]

How do I extend a room with a bigger one rather than adding another room? I wanted to have a big " warehouse" room.

[Impish Kat]

If I'm following what you are asking, there is no way to simply replace an existing room with another.  You literally have to delete the room (and all the items in it) and replace it with a new one. 

 

Your other option is to "add on" to the existing room.  Now that doorways can be placed side by side (but not on corners), you could add a hallway or another room and fill the gaps with doorways.  This will give you the appearance of a larger, open room.