Deleting A Category
You can delete a category by pressing "Delete category". The category in the centre of the screen is the currently selected category that will be deleted. You will be prompted to confirm the delete:
You can delete any category, including the categories that came with your app (you can restore the categories that came with your app using the Settings option later).
Note that the cards contained in the deleted category are NOT deleted when you delete the category. They are still present in the Items Library.