IS THE SYSTEM ON MY MAC UPGRADABLE?

A late-2009 through late-2011 iMac can be upgraded to High Sierra 10.13.6. See: How to get old versions of macOS - Apple Support

A late-2012 through late-2013 iMac can be upgraded to Catalina 10.15.7

A mid-2014 or later can be upgraded to Big Sur. See: How to upgrade to macOS Big Sur - Apple Support

The model year of your iMac is available at Apple menu > About This Mac

Back up your data, check your applications for compatibility, and depending on which iMac model you have, click on High Sierra, Catalina, or Big Sur.

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