how do i download Mac OS High Sierra?
Imac 21 inch mid 2011 running OS X Yosemite, how do I update to Mac Os High Sierra?
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iMac
The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.
With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. For Best results use Safari to commence the download as Others may not work.
Safari will open a redirect and open the Apple Store where the download can commence.
macOS High Sierra 10.13 hardware requirements
Make Time Machine Backup is very useful and can be used to Revert to Previous Working macOS
