This brings you to a screen that has several settings you can change for the installation. One of them is the Auto Upgrade checkbox. Check this to enable it.
After enabling the feature, click on the Edit Installation Details button. The feature will now be enabled.
How often will the program upgrade?
Softaculous has an automatic script, also known as a Cron job, that runs once every 24 hours. Among other things, such as automated backups (if enabled) this script runs the Auto Upgrade check so if any new updates are available, it will upgrade the program at that time.