The following quote is extracted from the FAQ page. It's about the subscription cancellation procedure:
Yes, you can cancel your subscription from the website member area by clicking on account setting and updating your subscription status to cancel from there. However monthly subscription you will need to continue for at least 3 months according to the rules of Avanset.com Billing Policy before being able to cancel it. If you want to cancel before 3 months, you can do it by paying $59.99 Fee for cancellation of your subscription immediately. Quarterly, Semi-Annual and Annual subscriptions can be cancelled any time from within your Avanset website member area.
As you can see, you need to connect to the Members Area and you can cancel it from there. For additional Support, check the folloing page: http://www.avanset.com/support.html