software update

Installing a newer OS is called an upgrade.

Which OS you can upgrade to will be governed by which model and year your mac is.

Click on the  top left of your screen click on About This Mac to find out the year of your mac.

For macOS Mojave or macOS Catalina,

Open Safari and click on this link, 

How to get old versions of macOS – Apple Support

Go to Check Compatibility to see if your mac qualifies for the OS upgrade you want.

Then go to the Download OS section and click on the OS you want to install.

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.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you want to or are able to install Big Sur, open Safari and click on the link below.

How to upgrade to macOS Big Sur - Apple Support

If you are considering upgrading to Catalina or Big Sur be warned they do not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see

if they are offering 64bit updates.

In addition the information provided by Eau Rouge, you'll need to make sure that your Mac is compatible with newer versions of macOS. You can identify your model of MacBook Air by clicking the Apple menu in the top left, then clicking About This Mac.

Identify your MacBook Air model - Apple Support

If your Mac was introduced in 2013 or newer, you can run the latest version of macOS, macOS Big Sur 11.5.

If your Mac was introduced in 2012, you can run up to macOS Catalina 10.15.7.

If your Mac was introduced in 2011 or earlier, you can't upgrade your Mac past macOS High Sierra 10.13.6.

"In addition the information provided by Eau Rouge, you'll need to make sure that your Mac is compatible with newer versions of macOS. You can identify your model of MacBook Air by clicking the Apple menu in the top left, then clicking About This Mac."

I mentioned that in my post.