Hello and welcome @HisFocus 
You can delete categories and subcategories from their category wrench menu. If you navigate to a category (eg. /c/general/4) you should see the wrench in the top right:
In there you should see the ‘delete category’ button on the general tab:
You would need to delete any subcategories first, as well as move any existing topics into other categories (apart from the About one), before it will let you perform the delete.
Does that help?