iMac (21.5-inch, Mid 2011)
My iMac (21.5-inch, Mid 2011) will not upgrade to the High Sierra 10.13.6
Question marked as
Top-ranking reply
Ir should be able to upgrade to High Sierra, what OS is the Mac running at the moment, click on the Apple top left, click on About This Mac, please share a screenshot. Your Mac must be running McOS X Mountain Lion or later in order to be able to upgrade to High Sierra. If you are running an older OS you will need to upgrade to El Capitan first.
How to upgrade to macOS High Sierra - Apple Support
How to upgrade to OS X El Capitan - Apple Support
Or are you experiencing a different problem?