STOP: Make sure you are completely prepared for the update. Please follow this guide to make sure you've followed all the preparation steps for you and your computer:
Upgrading Your macOS Start Guide
Sign In With Your Apple ID
Many features of macOS, including the App Store and FileVault, require an Apple ID. Before upgrading, log on to https://appleid.apple.com/ to make sure you know your username and password. You should also refresh your security questions and two-step verification settings if you haven't done so recently. If you have difficulty with this process, you will need to work with Apple Support directly.
If you not want to maintain an account with Apple, it is still possible to use macOS, but please contact the Helpdesk for potential limitations before you upgrade.
Upgrade Your Mac
This process may take about 1-2 hours, depending on your network connection. If you have a laptop, make sure your computer is plugged in to the power adapter during the upgrade.
Run Apple Software Update and click Upgrade Now.
Review Next Steps