How do I cancel my ProCamera Up subscription?

In the App Store App, tap the round user avatar in the top right corner; on your Apple Account page tap your account name > Subscriptions.

Here, ProCamera Up should be listed as an active subscription, including a button to cancel.

Another way is to go to https://apps.apple.com/account/subscriptions.

For additional information on this topic visit https://support.apple.com/en-us/HT202039.