Note: Account tax categories that are in use (e.g. configured on accounts and tax codes) cannot be deleted. In order to delete an account tax category that is in use, first check the References tab to determine what entities are configured to use the account tax category that you wish to delete and then change those entities to use an alternate account tax category.
Under the Account Tax Categories heading on the left select the account category you wish to delete
Under the same Account Tax Categories heading click the icon
On the confirmation dialog that appears select Yes