You can cancel your subscription at any time. When you cancel your subscription, you will continue to user Pro features until your subscription period is over.
How you cancel depends on which platform you've sign up on.
Apple (iOS)
Open the "Settings" app on your phone
Tap your Apple Account
Tap "Subscriptions"
Search for "GymRats" and tap it
Tap "Cancel"
Google (Android)
Open "Google Play" app on your phone
Tap your Google Account
Tap "Subscriptions"
Search for "GymRats" and tap it
Tap "Cancel"