How to reset magento admin password?

Login phpmyadmi, click SQL function button, and run:

UPDATE `admin_user` SET `password` = MD5(‘123456’) WHERE `username` = ‘admin’;

After that the new admin and its password is:
admin 123456

Very simple, just choose SQL button, and run the following sql sentence:
UPDATE `admin_user` SET `password` = MD5(‘PASSWORD’) WHERE `username` = ‘USERNAME’;

USERNAME – the user name which you want to update its password
PASSWORD – your new passwords.