Click on the plus and minus buttons. To make something appear or disappear, click on the button to put the furniture in. For example, clicking the blue + button under plants will add one plant. Note that you can only see the changes of any - button by clicking it, then the green flag. Also, there must be at least one of each item on the screen. I will update soon, but if you want none of an item on the screen, just drag it off the page. If saving doesn't work for you, you must be logged in, and your status must be Scratcher, not New Scratcher.
The idea, art, and scripting is all by me. If you use any of these, please give me credit. Remember that all information is stored on cloud variables. For example, if one person added 2 beds and 3 tables, the next person sees that, and they can add or subtract anything. The third person can see the changes that the second person made, and anyone can see the changes that anyone made when they look at the cloud variable.