MacBook Air upgrade

Okay. You can upgrade up to Monterey 12.6.5. You can get it here…

How to download macOS - Apple Support

Be aware older 32bit software will no longer run and may need updated or replaced. You can check for 32bit software with Go64.

https://www.stclairsoft.com/Go64/

Some older 64bit software may need updated or replaced as well.

Be sure to back up first.

You need a 2012 or later Mac to upgrade. which Mac (year) do you have?

What year is listed under the Apple Menu > About This Mac?

The 2018 MacBook Air wasn't available until Oct 2018.

You're welcome. Go64 is a free utility you install which just lists which 32bit software you may have installed.