When a new Strapi version is available, you'll see a notification in your admin panel. You can also check the Strapi GitHub releases page that is linked in the notification to see what's new in the latest version and take note of the latest version number.
Once we upgrade the Strapi dependencies and install again, you'll notice the notification is gone and when you check settings the version number has been updated. To update production, you push your changes to GitHub and run git push heroku HEAD:main
.