Live example;

Amanda from Bowtie Boutique already has a magento website before getting us to redo it for her, but she does not know the username and password for the admin user in the backend. She has a login but it does not have full admin access.

We need full admin access but she has no idea what the login is or the email address used to set it up therefore we couldn't just click on the 'forgot password' link.

This  tutorial taught me how to reset it in the database.

https://www.siteground.com/kb/how_to_reset_admin_password_in_magento/

You need access to PHPmyAdmin and cPanel to make the changes.