You can easily cancel your membership in your user account. To do so, go on the bottom left to the "My account" section. At the bottom of this section you will be able to see the option to cancel your membership. Please click on it and a new window will pop up where you can find the button to confirm your cancellation.
Cancellation is currently only possible in the browser, i.e. in the web version. It is currently not possible to cancel in the iOS & Android app.