1. Right click Elite Dangerous in your Steam library
2. Select ‘Properties’
3. Go to the ‘Local Files’ tab
4. Select ‘Browse Local Files’
5. Select the EDLaunch.exe
6. Login if required
7. Select Elite Dangerous: Horizons – Engineers Beta [2.1]
8. Witness how the Upgrade button is now blue and ready to ‘Upgrade’
9. Select the ‘Upgrade’ button and you should be good to go
From here: https://forums.frontier.co.uk/showthrea ... 509&page=4