A lost password can be a real headache, especially if it’s the admin account for an installation. It is possible to login without credentials or reset a password for any user from the command line using drush. Drupal.org discusses these operations.
To login to a Drupal installation as the admin user without knowing the credentials simply navigate to your site’s root directory and use drush uli.
# From site root drush uli
From there you can change the credentials or go about your work without changing the credentials.
It’s also possible to change the password for a user using drush upwd.
# Set a user's password drush upwd admin --password="mynewpw"