Android:
1. Visit https://play.google.com/apps/testing/com.contorra.golfpad and select to leave the testing program
2. Optionally leave the Golf Pad Beta Google Group at https://groups.google.com/forum/#!forum/golf-pad-beta
3. Uninstall the current version of Golf Pad and install it again from Google Play Store. Be sure to log in with a Golf Pad account before you uninstall and log in with the same account after reinstall, so that you playing history and statistics are preserved.
iPhone:
Use the link in email you received at the time you joined the beta program or select Stop Testing in Test Flight app on your phone.