I have a macbook air OS X El Capitan version 10.ll.g (13") but I don't remember when I bought it - possibly before 2012. I need to upgrade to Mojave or Catalina. Is it possible and is it risky to my computer?
MacBook Air 13″, OS X 10.11
How to upgrade to macOS Catalina - Apple Support
If your Mac predates the models eligible for Catalina read the links at the end, which describe how to upgrade to High Sierra or other macOS versions.
Is it risky? Not if you follow Upgrading macOS without fear - Apple Community. Zero risk whatsoever to your existing system.
Trying to upgrade
