So my MacBook Air under "About this Mac" is running OS X Mavericks 10.9.5, but under "Software Update..." thinks that macOS Sierra 10.12.1 is installed. I've tried rebooting to see if the system would update to Sierra, but it just stays at 10.9.5. App Store has no option for updating because it thinks Sierra already is installed. And my MacBook Air is Late 2010 so should be compatible with Sierra. Not sure what to do!

  • Look in the Applications folder for the Install macOS Sierra app and then double click to install. (Run a Time Machine backup first.) Perhaps the installer has only been downloaded, but macOS Sierra not actually installed. – IconDaemon Nov 27 '16 at 18:05

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