1) You MUST be using Alex's 3dxChat Extender. http://3dxchatextender.blogspot.fi/ All these steps are done in the Home Editor (Customize).
2) SAVE your room! Just in case! Click on Menu (Upper Right), then SAVE house layout.
3) So prepare your room, (clear out space, etc) to make room for the new
addon. (Some addons don't take much space, like the window blinds) Each add on is a part of a room. The description usually says where it fits into the room and which room. (Loft/Home#1) or (House/Home#2).
4) Load the addon. Click on Menu (Upper Right) and then either MERGE house layout or LOAD house layout. LOAD will CLEAR your room! Sometimes this is what you want. Most of the time you'll want to MERGE.
5) Load additional addons. Here you'd want to MERGE.
If you like my stuff, and find me in world, I'd love a gift!.