10. Update , update, update
Click on the Updates button in the App Store window to check if you have the most recent version of both macOS Sierra and any apps. If any updates are available choose Update All. This ensures a much smoother upgrade. If you’re not currently running macOS Sierra on your machine, you must make sure you have at least OS X 10.8 Mountain Lion before upgrading. Click Apple > About This Mac if you want to check your OS version. If you’re running OX 10.7 Lion, follow the steps at bit.ly/lion_to_high_sierra to install macOS Sierra on your machine before upgrading to High Sierra.