Manual:Resetting passwords

To reset admin´s password you should change the value of user_password field, in user´s table.

UPDATE user SET user_password = MD5(CONCAT(user_id, '-', MD5('somepass'))) WHERE user_name = 'someuser';

An option that worked on Windows was: Open a command prompt CD to the maintenance directory enter this command: php changePassword.php --user='username' --password='foo' 