If something doesn't quite work right after you've installed macOS High Sierra, you can reinstall the operating system so it is a fresh copy. Reinstalling a fresh copy of macOS High Sierra will not affect your current settings. Applications and settings will remain the same. Completing this process replaces the core files of macOS High Sierra in case something wasn't working right before.

Before you start: Back up your data

  • It is a good idea to perform one full backup before starting with a clean copy of macOS Sierra. You can also back up files and documents using a cloud-based storage system like Dropbox, OneDrive, or the easiest: iCloud.

  • Make sure the computer on which you're installing a fresh copy of macOS Sierra can be connected to the internet, either via Wi-Fi or Ethernet. This step is important. An Internet connection is needed in order to reinstall the macOS operating system.

  • If you are using a laptop, make sure it is connected to a power source.

How to install a new copy of macOS HighSierra in Recovery Mode

Recovery Mode is the special salvation of the Mac that first launched with OS X 10.7 Lion. It creates a temporary boot partition that allows you to access certain things on your computer that you might not be able to if your system froze or crashed. It is the easiest way to install a fresh copy of an operating system.

  1. Connect your Mac to the internet via Wi-Fi or Ethernet
  2. Click on the Apple icon in the upper left corner of your screen.
  3. Select Restart from the drop-down menu.

    Restart your Mac

  4. Hold down Command and R (⌘ + R) at the same time. When you hear the startup chime (or when the screen goes black on newer Macs), keep holding the keys until your computer reboots.
  5. Click on Reinstall a new copy of macOS.
  6. Click Continue.

    Reinstall macOS Sierra

  7. Click Continue again when the installer window appears.
  8. Agree to the software terms and conditions.
  9. Select your hard drive.
  10. Click Install.
  11. Complete the installation process.

    Reinstall macOS Sierra

How to download a fresh copy of macOS High Sierra from the Mac App Store

You can also start fresh by downloading macOS High Sierra directly from the Mac App Store. Remember, you must have an internet connection in order to download a fresh copy of the Mac operating system.

  1. Click on the Apple icon in the upper left corner of your screen.
  2. Click on App Store...

    Launch the Mac App Store

  3. Click on the Purchased tab in the Mac App Store window.
  4. Select macOS High Sierra from the list of purchased apps.
  5. Click Download.

    Download macOS Sierra

  6. Click Continue when asked to confirm that you want to install software that is already on your computer.
  7. Click install after macOS High Sierra is finished downloading.
  8. Complete the installation process.

Any questions?

Do you need help reinstalling macOS High Sierra on your Mac? Post your questions in the comments and I'll do my best to help troubleshoot your issue.