David
If you can’t login, but you can access your site via FTP, then edit the theme’s functions.php file and add this code to it, right at the top after the first<?php bit:
wp_set_password('MyNewPassword',1);
Put in your own new password for the main admin user. The “1″ is the user ID number in the wp_users table.
Then just log in using the new password, just make sure you remove the line...