The way my house is planned house is pretty awful (51 construction btw), and I want to change it. Only thing is, to change it will I have to remove the items already in the house and will that destroy them?

Certain items are destroyed when you remove them and some aren't. IF you mount an Amulet of Glory, Legend's Cape, or Anti-Dragon Fire Breath shield, then you get it back. Similarly, you get your Decorative armour back if you delete that stand. Basically, if it holds anything that you had to put in there (as in, a costume rack, for example), or if it holds an item that was put in the moment it was made (Legend's Cape, etc), then yes. Although I'm not sure if you recieve portraits back when you remove them. And if you delete the costume room without taking anything out of the furniture in it, then I've heard you lose all the items in it.