This software update can be downloaded by using Garmin Express. Please note that once a software update is released it can take up to 24 hours before Garmin Express provides this update to all users.
Quoted from this forum regarding Edge 20 software updates.
I know nothing about Garmin Express, and I haven't got a clue about what it is.
I have had Garmin devices for many many years and have always used Garmin Web Updater.
Works for me. ;)
Thanks,
Mick.