The steps depend on where you purchased your subscription.
Apple App Store
Open Settings on your iPhone or iPad.
Tap your Apple ID.
Tap Subscriptions.
Select Rebrand.
Tap Cancel Subscription.
Google Play
Open the Google Play Store.
Tap your profile icon.
Select Payments & subscriptions.
Tap Subscriptions.
Select Rebrand.
Tap Cancel subscription.
Canceling prevents future renewals. You can continue using Premium until the end of your current subscription period.