MacBook Air

Back up your data, check the application compatibility table, click here, and then on the download link for a more-recent OS. Your computer needs to be a 2012 or newer one to run Catalina.

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

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Just confirming what Neil has already said, your Mac needs to be 64 bit capable to run most apps out there today.