How to change root admin user password in Drupal ?

In order to reset the root or superadmin password on a drupal system, login into the database by looking at the settings.php. You can use phpMyAdmin or any other MySQL utilities like SQLYog, or MySQL command line.

Run the following query to reset the password.

UPDATE users SET pass = MD5('password') WHERE uid = 1 

The user id of administrator is always 1.
Password field in drupal is stored as MD5 of the actual string password. So running the above query would set your password as password of the superadmin user.