If you are not a Mac user or you are a windows user (and want to install Sierra in VirtualBox, Vmware or any other virtual machine) then you can download the file from the below link: Download MacOS High Sierra (from apple site) How to install MacOS High Sierra on Virtual Machine. Thankfully, Macs include a tool that make backups easy: Time Machine. Learn how to back up your Mac. Download and install. MacOS High Sierra is available as a free update via the Mac App Store.

Check compatibility

You can upgrade to macOS Sierra from OS X Lion or later on any of the following Mac models. Your Mac also needs at least 2GB of memory and 8.8GB of available storage space.

MacBook introduced in late 2009 or later
MacBook Air introduced in late 2010 or later
MacBook Pro introduced in mid 2010 or later
Mac mini introduced in mid 2010 or later
iMac introduced in late 2009 or later
Mac Pro introduced in mid 2010 or later

To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu . If your Mac isn't compatible with macOS Sierra, the installer will let you know.

Make a backup

Before installing any upgrade, it’s a good idea to back up your Mac. Time Machine makes it simple, and other backup methods are also available. Learn how to back up your Mac.

Get connected

It takes time to download and install macOS, so make sure that you have a reliable Internet connection. If you're using a Mac notebook computer, plug it into AC power.

Download macOS Sierra

For the strongest security and latest features, find out whether you can upgrade to macOS Catalina, the latest version of the Mac operating system.

If you still need macOS Sierra, use this link: Download macOS Sierra. A file named InstallOS.dmg will download to your Mac.

Install the macOS installer

Download Os Sierra Installer

Double-click the downloaded file to open a window showing its contents. Then double-click the file within, named InstallOS.pkg.

Follow the onscreen instructions, which will guide you through the steps necessary to install.

Begin installation

After installation of the installer is complete, open the Applications folder on your Mac, then double-click the file named Install macOS Sierra.

Click Continue and follow the onscreen instructions. You might find it easiest to begin installation in the evening so that it can complete overnight, if needed.

Allow installation to complete

Mac os x 10.6 8 full download. Please allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both macOS and related updates to your Mac firmware.

Learn more

Download High Sierra Installer

• If you have hardware or software that isn't compatible with macOS Sierra, you might be able to install the previous version, OS X El Capitan.
• macOS Sierra won't install on top of a later version of macOS, but you can erase your disk first or install on another disk.
• You can use macOS Recovery to reinstall macOS.