I’ve arranged this book in logical order, and I recommend performing these steps in the order I present them. You need not learn every last detail, but I hope you’ll at least skim the whole thing.
Start on the right foot:
Discover what you have to look forward to when you upgrade to High Sierra, as well as what features were added (and removed) in the last several upgrades. Read Catch Up with macOS Changes.
Follow the strategy you selected earlier to run the High Sierra installer, choosing all the optimal settings and options, and making sure all your personal data is still in place afterward. You’ll do one of the following:
Perform Post-installation Tasks, such as responding to login requests, installing updates to macOS, and tweaking preferences. You’ll also deal with any surprises that may occur along the way.
Problems? If your computer isn’t working properly after the upgrade, don’t panic. See Troubleshoot Upgrade Problems.