The System Updater is optimized for devices running Windows 7, Windows 10, Sierra, El Capitan, or Yosemite. To determine what OS you’re on: Click on the Apple icon in the top left corner of your screen. From there, you can click ‘About this Mac’. You’ll now see a window in the middle of your screen with information about the Mac you’re using. Click on the Start button. In the search box, type Computer. Press and hold or right-click Computer, and then tap or click Properties. Then look under Windows edition for the version.