Categories can be deleted at any time. One thing to keep in mind is that when deleting a category not all related expirations are deleted. This is because in specific cases you don't need the category to show up in reports but would like to keep any existing expirations for auditing purposes.
Deleting the expirations first
If you'd like to delete the expirations for that specific category, first click on Expirations on the top menu and then do a search of all expirations with that specific category.
Select all the expirations from the search results and from the bulk edit tool click on the trash icon.
This will delete all the expirations.
Delete the category
To delete the category, click on Your Account on the top menu, then on Settings and then on Categories from the left menu.
From the category list, click on the black arrow pointing down and from there click on Delete.