You can cancel your membership at anytime. A cancellation means that no future rebill will be
charged your account. You can do this from from Clickbanks Order detail form. You will need your order number as well as your Email address. Once you have entered these details, select "I would like to cancel my subscription or Membership" from the What problem are you having option.
Send that ticket out and Clickbank will take care of that for you. If you have any further questions please create a support ticket and We will help you out. We can also be the ones canceling your account if you have any doubts about how to proceed.