These instructions are for subscriptions paid for via the Google Play Store only.
On your Android device, go to your subscriptions in Google Play.
Select the subscription that you want to cancel.
Tap Cancel subscription
Follow the instructions
Deleting / uninstalling fieldmargin will not cancel your subscription.
If you subscribed via in-app purchase you can find instructions for Apple here and if you paid via fieldmargin.com you can find instructions here.