Update

kency34 Said:

"Update: Why I can't update Macos Version 10.13.0 on my MacBook Air ?"

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A Screenshot would Help:

What happens what you try? Any error messages? Please provide a screenshot of the error message, to get the answer you need.

1. Go Here: Take a Screenshot on your Mac - Apple Support
2. Use this Method: How to capture a window or menu
3. Reply: With that screenshot in included in the reply

To learn how to update macOS, please read Keep your Mac up to date - Apple Support.

To learn how to upgrade macOS to the latest version, please read How to upgrade to macOS Catalina.

Exactly what model/year is your device?