Log in to your Blockbuster account using your email address and Blockbuster password.
Click on the "My Account" link near the top right corner of the page.
Click on the "Cancel" link, which is under the "Subscription Plan" section. Follow the directions that appear. Give the reason you want to cancel your membership to Blockbuster, as well as any other information requested.
Return any movies and games you have at the end of your membership period to Blockbuster by either mailing them or returning them to a participating Blockbuster store to avoid charges to your credit card.