K2 Demo Category

When I trash or unpublish Demo Category in K2, template doesn't work. Frontend opens with 404 error. I want to create and use new categories but I can't, because only Demo category is displayed.

First create new category , then swap to it in home page menu item settings , then delete category from k2. What happens is that you delete category and home page it set to point to it, so first point home page to something else.