To make Multi Commander check for beta release at startup you need to activate that in its configuration
In the configuration for "Core Configuration" (located under the "Configuration" menu) there is a check box.
"Check for and download and update of beta version of available"
If this is checked Multi Commander will look for a new Beta Version at startup.
If you do not what to always check for beta version at startup you can also update to the latest beta version by running the MultiUpdate program separately. And in the settings for MultiUpdate there is a checkbox for "Download unstable beta if exists".
BUT.....
Beta release are to be considered unsafe. They contain feature and fixes that are not yet fully tested. So test them at your own risk
