Your Mac must already be running OS X 10.7.5 or later.
Scroll to the section for older versions and select the macOS Sierra 10.12 link. download macos sierra 1012 dmg file install
If you have previously downloaded Sierra, or if your Mac is compatible, you can try the official link. Your Mac must already be running OS X 10
Technical Support Team Document Version: 1.0 or if your Mac is compatible
Note: Apple changes these links occasionally. If the link fails, use Method B.