You can cancel your subscription by contacting support: http://www.dilbertfiles.com/contact/?support
From their FAQ: You will have to include the email address you used to sign-up with and indicate that you would like to cancel your account. We will ensure that your subscription will not be automatically renewed after the current subscription period ends.
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.