If you have an old user account on your Mac that you can no longer access, there's a way you can still get into it as long as you have an "Administrator" account on that Mac. Just get into the System Preferences from the Apple Menu and click "Users & Groups". Then click the lock icon and enter the admin name and password. Select a user, and then click "Reset Password".
Sarah accidentally spilled wine in her computer, so she's ordered a new one. She's borrowing a computer from a friend in the interim. She has a variety of email accounts though, and she wants to access those, but she doesn't want to leave her account information saved on that computer. Sarah should create her own account on that PC. Then, before she gives back the computer, she can just delete that account. Sarah can just go into Users section of Control Panel and make a new account with administrative privileges. Then log out of her friend's account, and log into that account.
It should go without saying that having a current backup of your computer is an essential preventative measure in case the worst happens. But there's another very simple step you can take that can potentially save you a lot of headache -- create a secondary administrator account. Make sure that account is pure and is in the default Mac or Windows configuration.
Michael wants to know how he can downgrade his account to a "limited user" as opposed to running as administrator in Windows. Leo says he'll have to create an administrator account first, and then in the Windows user account settings he can downgrade any user account. Should he run as "Guest"? Leo says no, "guest" will automatically delete all the data every time the user logs out. He can just downgrade his current account after logging into another administrator account.