How to upgrade to 10.12 version

Click on the blue words in Neils reply, these are links that will take you to the Applications compatibility table and the Sierra download link.

Is there a reason that you want macOS Sierra 10.12.6, it is a very old OS now and does not have updated security protocols.

Your 2015 MacBook Air can upgrade to all available OS's including the latest macOS Big Sur 11.14.

If you want to upgrade to newer OS's like macOS Mojave 10.14, macOS Catalina 10.15, 

macOs Big Sur 11.4 I would recommend you upgrade to macOS High Sierra 10.13 first.

For macOS High Sierra 10.13, macOS Mojave 10.14 and macOS Catalina 10.15,

Open Safari and click on this link, 

How to get old versions of macOS – Apple Support

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.

Back up your data, check your applications for compatibility, and click on Sierra.

(200949)

1. Click on those words above.

2. The version you're asking for.

(200950)