How to update an older iMac to recent OS.

Which iMac do you have? That will determine how far you can upgrade the OS.

You can find your Mac's name and model year in the About This Mac dialog in the Apple () menu. (Model name and year are sufficient – don't post the serial number.)

Back up your data, check the application compatibility table, click here, and then on the download link for a higher OS.

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

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Niel wrote:

From the original message: iMac 27″ 5K.

This identifies it as a 2017 or newer model.

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The first 27" 5K Retina iMac came out in Late 2014.

• The Late 2014 and Mid 2015 ones can run Big Sur, but nothing later.
• The Late 2015 one can run Monterey, but nothing later.
• The 2017 one can run Ventura, but nothing later. (The 2017 iMac Pro will be able to run Sonoma.)
• The 2019 and 2020 ones can run Ventura, and will be able to run Sonoma.

From the original message: iMac 27″ 5K.

This identifies it as a 2017 or newer model.

(244687)

Given that this one has High Sierra installed, we can rule out it being a 2019 or 2020 model. It could be any of the others.