First, login to your Cleeng account via https://cleeng.com/my-account - this account was automatically created when you purchased your subscription - use the same email and password to log in.
Once you are logged in you will see your library with your purchase history. Click on the second tab titled "Subscription." This will show a full list of all your active subscriptions.
In the fourth column you can easily change the subscription status by hitting “Stop.” The change will be saved automatically and your subscription will be cancelled.