Ho w to Install the macOS High Sierra beta
Enroll your Mac
With your Mac started up from the clone, sign in at beta.apple.com, click “macOS”, and click “enroll your Mac” under Get Started. On the next page, download and install the public beta access utility.
Close the beta access utility installer and the App Store will open to a High Sierra beta page. Click the button on its left side to download the actual installer for the beta; it’s more than 5GB large, so it may take a while.
Install the beta
When the installer opens, run through its steps, then wait. Just make sure the “High Sierra” volume is set as the destination. You can opt out of the new Apple File System, but doing so defeats a reason to try the beta.