To stop your paying subscription is simple, you have complete freedom over your account and your settings. After you log in, go to your account settings by clicking the link in the top right corner. Then click on the "My Preferences" button > then the Account settings tab > here you simply press on the unsubscribe button.
Your account with be automatically transformed into a Free account at the end of your current subscription period. This ensures that all of your information and data remains intact. You can continue to use your account as a Free user.
You can upgrade again at any time. You alone determine the use of your account and are free to choose when you subscribe and when you stop your subscriptions.