On the web app
You can cancel your premium subscription anytime by going into Settings > My Account and clicking on the Subscription tab.
When you cancel your subscription, you’ll continue to have access to your account until the end date of the current subscription term. We won’t charge you the following year or month, but we’re unable to refund any charged monthly or annual fees. Read more about our refund policy.
On the mobile apps
Unlike those purchased from the web app, subscriptions purchased from the iOS or Android app are not recurring. You must actively renew your subscription each year to maintain your premium status. This means that if you decide to end your subscription after the first year, you don't need to take any action. You won't be charged for the next billing cycle unless you go to the App Store (iPhone or iPad) or Google Play (Android) and pay for a new subscription.
To read about our refund policy for subscriptions purchased from a mobile device, see this article.