To modify or cancel an auto-renewing membership please follow these steps.
- On your iPhone, iPad, or iPod touch
- On the Home screen, tap Settings.
- Tap App and iTunes Stores.
- Tap your Apple ID.
- Tap View Apple ID. You might need to sign in.
- Under Subscriptions, tap Manage.
- If you don't see a subscription in iTunes and are still being charged, make sure that you're signed in with the correct Apple ID.
- Tap the subscription that you want to manage.
- Use the options to manage your subscription. You can choose a different subscription period, or turn off Automatic Renewal.
- Turn off Automatic Renewal to cancel a subscription. Your subscription will stop at the end of the current billing cycle.
For more information please refer to to the following link.