Use a Second External Hard Drive at least 1.5 times the size of the InternalHard Drive. Proceed: from there as necessary with the InstallĬreate a Time Machine Backup of your Mac, that way you can have something to restore your Mac from, should anything go wrong with the install, and to migrate it all back.Plug in: the High Sierra USB Bootable Installer.Boot: into Recovery Mode: Hold Down upon boot.Use: The in Terminal In Catalina to create this for macOS X 10.12 Sierra.

Go Here: How to Create a Bootable Installer for macOS - Apple Support.

Reinstall the Mac OS that was Previously Installed. It needs to be at least a 2012 one, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card, to run a newer OS. Use an External Hard Drive at least 1.5 times the size of the Internal Hard Drive.ī. Back up your data, check your applications for compatibility, and if your Mac model is recent enough, click on Mojave, Catalina, Big Sur, or Monterey. Use a USB Bootable Installer to create It.Ĭreate a Time Machine Backup of your Mac, that way you can have something to restore your Mac from, should anything go wrong with the install, and to migrate it all back. I need the old version in order'Ĭreate a Time Machine Backup. Edit: The full installer is an app that will be downloaded from the App Store It will be a 'Install macOS High Sierra' app (around 5.25 GB) in the Applications folder and it will automatically.

How can I do it? I tried to use Airport from my iMac so I can be able to install Mojave, and it couldn't fine my Mid 2015 MacBook Pro. ' Mac OS High Sierra: I couldn't downgrade my Mid 2015 MacBook Pro to High Sierra. For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac.

Mac high sierra