It depends on which service you want to deactivate/unsubscribe from.
If you want to deactivate your Premium account, you can do so here http://twittercounter.com/pages/settings/premium.
If you want to cancel your Featured User account, you can do so via the "Manage Subscriptions" tab on your Featured User report page (the link to this page was sent on signup). All the necessary instructions are there.
If you'd like to unsubscribe from the newsletter you can do so by clicking "Unsubscribe" in the newsletter.