Select the MacOS you are using:

Pre-MacOS Sierra (Mountain Lion, Mavericks, Yosemite, El Capitan)  >> Click here
MacOS Sierra (released 09/2016) and High Sierra  >> Click here

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How to check your MacOS version?

  1. Click on the Apple icon in the top left corner of your screen.
  2. Click on “About this Mac“.

You will see a popup with your OS and its version.