If you own a Mac, your computer can have multiple administrators, and dozens of users, groups, and guests with varying account privileges and settings.
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How to delete a user on a Mac using System Preferences
First of all, make sure you're logged into an administrator account.
1. Click System Preferences from the app menu at the bottom of your screen (the icon resembling silver gears), or open it by clicking the Apple logo in the top-left of your screen and selecting "System Preferences…"
2. Next, find "Users & Groups" in the System Preferences menu (it is an icon depicting two people), or search for it in the search bar at the top.
3. Click the lock at the bottom of the screen to unlock the page. You may need to enter your password to do so.
4. Select the name of the user you wish to delete.
5. Click the minus icon at the bottom of the menu.
6. A pop-up menu will ask what you want to do with the user's home folder (the folder where all their files are stored, like documents, downloads, and pictures) — you can choose to delete it, save it in a "Deleted Users" folder, or let it remain in the "Users" folder.
7. Once you've chosen an option, select "Delete User."
8. The user has now been deleted. Be sure to click the lock at the bottom right-hand corner of the screen to ensure no other changes can be made.