Go to the HBO NOW app on your phone or tablet (and sign in if needed). Tap on the hamburger menu and go to Settings > Billing Information. Tap the “cancel subscription” switch, and confirm that you really want to cancel your subscription.
How do I cancel my HBO now account?
To watch all the episodes of your HBO NOW for free, you’ll need to cancel your subscription.
After you cancel your subscription, you’ll be able to watch all of your episodes without interruption, without having to sign in to HBO NOW.