How To Update Macos High Sierra 10.13.6 To 10.15 ((install)) -

Use the built-in Time Machine tool to create a full system backup to an external drive. This is your safety net if the installation fails.

To update your Mac from macOS High Sierra 10.13.6 macOS Catalina 10.15 how to update macos high sierra 10.13.6 to 10.15