How to Turn Off iOS Subscription Auto-Renewals from a Computer

By default, your subscriptions will auto-renew unless turned off at least 24 hours before the auto-renewal is due. 

• Open iTunes.
• If you're not signed in, go to Store > Sign In and enter your information.
• Go to Store > View my Account. You might need to enter your password again.
• On the Account Information page, scroll to the Settings section.
• Click Manage next to Subscriptions.

• Choose the subscription you want to manage.
• Use the options to manage your subscription. You can choose a different subscription period, or turn off Auto-Renewal.

Source: https://support.apple.com/en-us/HT202039