A factory reset will put your machine back to an immaculate factory state, as if it was fresh out of the box, with a clean and working install of macOS. There are a number of reasons that you may want to reset your Mac to its factory settings. Maybe you're selling it and want to wipe your data off of it. Perhaps it's infected with a virus. Maybe it's not working properly.
We can backup your data first or go directly to the factory restore steps.
Performing a factory reset deletes all your data and cannot be undone, you may want to back up your files first to an external hard drive or a USB storage device.
To reinstall macOS, you must be connected to the Internet.
If you are using a portable computer, make sure your power adapter is plugged in.
2. macOS: Set Up Time Machine
Time Machine is the built-in backup feature of your Mac. To use it, you need one of these external storage solutions, sold separately:
External hard drive connected to a USB, FireWire, or Thunderbolt port on your Mac
Time Capsule or macOS Server on your network
External hard drive connected to the USB port of an AirPort Extreme Base Station on your network
When you connect an external hard drive directly to your Mac, you might be asked if you want to use the drive to back up with Time Machine. Click Use as Backup Disk. If you select the option to encrypt, your backups will be accessible only to users with the password.
If Time Machine doesn't ask you to choose a backup disk when you connect the drive to your Mac:
Choose Apple menu > System Preferences.
Click Time Machine.
Click Select Backup Disk, Select Disk, or Add or Remove Backup Disk.
Select a backup disk from the list, then click Use Disk.
For additional backup security and convenience, you can repeat these steps to add another backup disk. For example, you might use one backup disk while at home, and another backup disk while at work.
3. macOS: Create Time Machine Backup
Choose Apple menu > System Preferences.
Click Time Machine.
To back up now, choose Back Up Now from the Time Machine menu.
Your first backup may take a long time, depending on how many files you have.
You can continue using your Mac while a backup is underway.
4. macOS: Open macOS Utilities
In the menu bar, choose Apple menu > Restart.
As your Mac restarts, hold down the Command and R keys.
Let go of the Command + R keys once the macOS Utilities window appears.
5. macOS: Erase Disk
Erasing the disk removes all the information from the disk. Be sure to back up the information you want to keep to an external device.
From macOS Utilities, select Disk Utility, then click Continue.
Select your startup disk on the left, then click Erase.
Enter a Name.
Click the Format pop-up menu, choose Mac OS Extended.
Click Erase.
After the disk is erased, choose Disk Utility > Quit Disk Utility.
6. macOS: Reinstall macOS
From macOS Utilities, select Reinstall macOS, click Continue.
After the computer reboots, Click on Continue.
Click Continue to verify your computer's eligibility.
Click Agree to accept the Terms of Service.
Click Agree to confirm you agree with Terms of Service
Select a Drive to install macOS on and click Install.
Install will now start and this will take some time. The computer will reboot during this process.