IOS update
my macbook air current IOS is OS X, 10.11.6. How to update the IOS?
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Did you already check, if your MacBook Air can be updated any further?
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Check compatibility
The version of macOS that came with your Mac is the earliest version it can use. For example, if your Mac came with macOS Big Sur, it can't use macOS Catalina or earlier. If a macOS isn't compatible with your device, the App Store or installer will let you know. If you try to install a macOS that is older than the version currently installed, the installer will say that it is too old to be opened on this version of macOS.
- macOS Big Sur 11 hardware requirements
- macOS Catalina 10.15 hardware requirements
- macOS Mojave 10.14 hardware requirements
- macOS High Sierra 10.13 hardware requirements
- macOS Sierra 10.12 hardware requirements
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copied from: How to get old versions of macOS - Apple Support
If so, use the links in this article to install macOS, by opening the article in Safari, otherwise the links will not work correctly.