Option 1
1. Open Mail app
2. From the "Mail" menu, select "Settings..."
3. Select "Accounts," and then highlight the account you want to delete.
4. Select "-."
5. When prompted, select "Remove" or "OK," then exit out of the Mail preferences window.
Option 2
1. Click Apple menu and select System Settings.
2. In the left pane, click on Internet Accounts.
3. In the right pane, click on the Mail account you would like to remove.
4. Click the Delete Account button at the bottom. (Please note that this removes your email account, but does not delete it.)
5. When prompted if you are sure you want to delete, select OK.
