Hi there,
First you need to install 10.11 to get access to the App Store...
These older macOS versions are available as disk images that you can download using your web browser. To get the installer from the disk image, you must use a Mac that is compatible with that macOS.
- Use these links to download a macOS disk image (.dmg) file. If these links don't work as expected, try again using Safari, which is in your Applications folder.
- Double-click the .dmg file to open it and see the package (.pkg) file within.
- Double-click the .pkg file, then follow the onscreen instructions to install the macOS installer into your Applications folder.
- Open your Applications folder and double-click the macOS installer, named Install [Version Name]. Follow the onscreen installation instructions.
Use a bootable installer
A bootable installer can be useful if you want to install macOS on multiple computers without downloading the installer each time, or when you can't install using macOS Recovery or the other methods.
To download an installer suitable for creating a bootable installer, use the App Store or use a web browser to download from a compatible Mac. The Mac must also be using the latest version of macOS Sierra or later.
How to create a bootable installer for macOS
If you need help
If an error occurred while updating or installing macOS
If you need more storage space to download or install
If your Mac doesn't start up all the way
