Can you update iMac from 2011

Yes. A 2011 iMac can run High Sierra, 10.13. You can get it here: macOS High Sierra 10.13

If you've installed and run any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac uninstall them according to the developer's instructions before upgrading to High Sierra.

Back up your data, check your applications for compatibility, and click on El Capitan or High Sierra. It's not capable of Mojave or above.

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