If you have access to the database directly (through phpMyAdmin or some other means), you will have to execute a query to change the super-administrator password.
First, you will need an MD5 hash of the password you want to use. Go to this website, and type the text you want to use for the password, click the button, and you will be gifted with the MD5 hash string.
Next, log into your database. You'll need to execute the following query against your Drupal database to reset the admin username and password:
Query syntax may change slightly if you aren't using MySQL:
UPDATE `users` SET `name`='your login name',
`pass`='your password in MD5 hash form' WHERE `uid`=1;
You should be able to log with the admin credentials you specified at this point.