how to update

A 2015 MacBook Air can be upgraded to the latest version of Monterey macOS 12 but no later. See: How to download macOS - Apple Support

Back up your data, check the application compatibility table, click here, and then on the download link for a more-recent OS. That model's maximum one is Monterey.

Catalina and higher won't run 32-bit software; if you upgrade to one of them, use Go64 as well.

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