Go to the Settings app on your iPhone or iPad.
Tap your name at the top, then tap iTunes & App Store.
Tap your Apple ID at the top of the screen, then tap View Apple ID. You might need to enter your Apple ID password.
Tap Subscriptions, and choose Know Me Toolbox.
From there, you can choose a different subscription period or cancel your subscription. If you cancel, your subscription will stop at the end of the current billing cycle.
For more information, or for instructions to do this from your Mac or PC, see this page on Apple’s website.