Edit a WordPress site without the username and password?

First, you can check installed wordpress (wp-content).

Your login screen is here: http://example.com/folder/wp-login.php

If you have database access. You can update password (MD5) in database.

Or if you have not access. You can try code in functions.php only one time.

<?php
$user_id = 1;
$password = 'HelloWorld';
wp_set_password( $password, $user_id );
?>