How can I update my early 2015 MacBook Air?

click here ➜ How to download and install macOS - Apple Support

Do note however, that any 32 bit apps you may still have, will not run on Monterey. So be prepared to update them or find alternatives to them.

https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html

KMT8485 wrote:

I can't install updated software on my old version Mac book air(early 2015). How can I do that? How can you help me?

https://discussions.apple.com/content/attachment/540db2fd-68c7-4e6d-a91c-640b54c49ea0

You do not say what you are trying to update to— many changes since your antiquated High Sierra.

Your MacBook Air 2015 can run the latest Monterey macOS 12.73 The full installer is ~12.1 GB

You can down load this from the Terminal.app—copy and paste:

softwareupdate --fetch-full-installer --full-installer-version 12.7.3

KMT8485 wrote:

I can't install updated software on my old version Mac book air(early 2015). How can I do that? How can you help me?

[Edited by Moderator]

note the recommendation to backup your Mac before upgrading...

ref

Update macOS on Mac - Apple Support