How to delete existing user accounts on your Mac for each person that doesn't intend on using the computer anymore.
2. Delete User Profile
You must be signed into the primary or administrator account to be able to delete user accounts.
Click the Apple menu (1), then click System Preferences (2).
Click Users & Groups.
If necessary, click the lock icon to unlock the settings of this window. You will be required to enter your Mac's administrator password.
Click on the user account you would like to remove to highlight it, then click the Remove button beneath the list of users.
If the user account you wish to delete is currently logged in, you will be unable to select it.
A confirmation prompt will appear. Select what you want to do with the user account's home folder:
Save the home folder in a disk image: This archives all the user's documents and information so the user can be restored later if needed. The disk image is saved in /Users/Deleted Users/.
Don't change the home folder: The user's documents and information remain and the user can be restored later if needed. The home folder remains in /Users/.
Delete the home folder: The user information is deleted and the storage space is freed.
If you don't delete a user's home folder, you can restore the user and the contents of the home folder.
Once you have made your selection, click Delete User.