Hello,
Make a full backup of your Site first before installing another Demo to the existing Site. Installing another Demo would reset all the Theme settings, and there is no option to set them back.
If you want to remove specific things from your current Demo then you can check and uncheck the options under the Remove Content accordingly: https://snipboard.io/4uhoSE.jpg
But if you want to use another Demo like Decor you mentioned then we would suggest you to Remove all Content and then import another Demo using WoodMart > Prebuilt websites.
Hope this helps !
Best Regards