Need assistance to update MacBook Air to Ios 11

The MacBook cannot run iOS. That is for iPhone/iPad.

You should be looking to upgrade macOS.

So that we can help you best, please tell us which Mac, model and year you’re having trouble with, and what macOS version you’re running. Find that info by clicking the Apple menu () at the top-left of your screen and then select About This Mac. (Note- for privacy and security reasons, please never post your serial number.)