can we upgrade mac book air from 2014

A 2014 MacBook Air can be upgraded to the latest version of Big Sur macOS 11 or earlier but no later. See: How to download and install macOS - Apple Support

Be aware that if you upgrade to Catalina 10.15 or later you will also need to update any non-Apple 32-bit apps. See: https://www.stclairsoft.com/Go64/

or

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

Also see the following from Identify your MacBook Air model - Apple Support

MacBook Air (13-inch, Early 2014)

Model Identifier: MacBookAir6,2

Part Numbers: MD760xx/B, MD761xx/B

Newest compatible operating system: macOS Big Sur

MacBook Air (11-inch, Early 2014)

Model Identifier: MacBookAir6,1

Part Numbers: MD711xx/B, MD712xx/B

Newest compatible operating system: macOS Big Sur