How do I update my MacBook Air to a 64Bit?

I think if you read this it will be a bit clearer what that is all about. There isn't really anything you need do except make sure your apps will work with 64 bit. That's mostly a matter of getting updates that work with 64 bit..

32-bit app compatibility with macOS High Sierra 10.13.4 and later - Fairly complete FAQ - https://support.apple.com/HT208436

Good news if the profile above for you is accurate. The computer is already 64 bit.