Update from 10.9.5

Look in your Applications folder for Install macOS High Sierra.app, move it to the Trash, empty the Trash.

connect your mac to your router. Restart your mac,

Open Safari do not use Firefox.

Click on this link,

How to upgrade to macOS High Sierra - Apple Support

Go to Section 4 and click on Get macOS High Sierra,

this will redirect you to the App Store High Sierra download page,

it should now say Get or Download.

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

The App Store Purchases does not show previous purchases/ downloads of macOS's

Sierra, High Sierra, Mojave and Catalina if you have ever purchased/ downloaded them.

Older Mac OS X's El Capitan, Yosemite and Mavericks are still displayed.

If you have a mac running Mojave or Catalina the App Store no longer

shows any previously purchased/ downloaded mac operating systems.

Back up your data, check your applications for compatibility, and download High Sierra. Your computer isn't capable of Mojave or above.

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You only have to download it and Apple assume it's "installed" even if you didn't. Ignore the App Store label and either retrieve the installer you downloaded once, or download it again from the Purchases tab of the App Store.

ggancz Said:

“Update from 10.9.5: I currently have version 10.9.5 installed and I want to update it to the latest version. How do I do so, and if it is not compatible, what can I do? I have a 2011 MacBook Air.”

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Just Upgrade:

If it is incompatible, then get you always have the option to get a new Mac. 32-bit applications are incompatible with Catalina. So, contact the developer if you were to upgrade, making sure they have a 64-bit option for you.

It's referring to the installer. Choose Applications from the Finder's Go menu and run or delete it as desired.

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