: Follow the on-screen prompts. This will not install the OS yet; instead, it places a file named "Install macOS Sierra.app" into your Applications folder.
You can download the disk image (.dmg) file directly from Apple's servers using a web browser, preferably . download macos sierra 1012 dmg file install
: Before starting, it's highly recommended to back up your Mac. Use Time Machine or another backup method to ensure your data is safe in case something goes wrong during the installation process. : Follow the on-screen prompts