iMac late 2015 upgrade

Back up your data, check the application compatibility table, click here, and then on the download link for a higher OS. That computer's maximum one is Monterey; if you want a version above that, you'll need a newer model.

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

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Anna_Aio wrote:

Do you know also if it would be possible instead of a newer model change some parts? For example use an external hard drive and run the system from there.

I am sorry I know and understand only a few things about these.

Changing parts will not change the answer as to the highest version of macOS you can run: Monterey. But if you would like to install Monterey on an external drive, and run it from there, you can do that.

For someone who only had a mechanical HDD, or Fusion Drive, installing macOS on an external SSD and running it from there might be a way of improving performance. I could be mistaken, but it looks to me like your iMac has an internal SSD which would be faster than any external USB 3 / SATA SSD that you could buy.

In any event, I would recommend backing up your system before you install Monterey.

From above: That computer's maximum one is Monterey.

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1. Click on it and look up the software you're using.

2. No.

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