macOS High Sierra requirements
You need MacBook or iMac going back to 2009, MacBook Pro and Mac Mini’s from 2010. You need to be running Mac OS X 10.8 or later. You need 5GB of available storage.
Back up your Mac before upgrading; go to support. apple.com/en-gb/HT201250 for advice on using Time Machine. Go to the Mac App Store and download the free macOS High Sierra upgrade.