1. Check your Mac compatibility
If your Mac is already running macOS Sierra then it should be
able to run High Sierra. If you’re not certain which OS you’re using, click on the Apple at the top left of your screen, then About This Mac. Click the Overview tab to check you’re running macOS 10.12. If you’re using a different OS, you may still be able to upgrade. Check your Mac model in the Overview tab – for example, Mac Mini Late 2012. Once you know the exact model of Mac you have, check the Apple Support website (bit.ly/model_compatibility). If it’s listed as compatible with macOS Sierra, you can install High Sierra.