Once you're ready to upgrade, click on the Apple logo in the top left corner, select App Store, click on the banner for macOS High Sierra and click install.High Sierra Electronics Headquarters High Sierra Electronics, Inc.The other problem is that the High Sierra firmware checker will only check to see if your system matches the signature on the server. And there's no way to check if your system has a specific zero-day vulnerability or not. The problem, according to the paper, is that even if you apply the latest OS upgrades you may not get the EFI update you need.
It would appear it is only the Mac Pro 5.1 machines that are needing the firmware update. We are getting reports (thanks Mick Corey) that when Mac Pro 5.1 owners are installing macOS 10.13 High Sierra that Apple is updating the Firmware as part of the High Sierra install.
