The phpMyAdmin way

Browse into the wp_users table in your database. Find your username and click on the edit icon () next to your username.

On the edit page, select MD5 from the Function dropdown next to the user_pass row. Change the value on the user_pass row to your new password and then hit Go.

Now log into WordPress with your new password and it will upgrade your password to the new phpass hashing.

The SQL query way

This applies where your database is wordpress and your login name is admin. Replace PASSWORD with whatever you want your new password to be.

UPDATE `wordpress`.`wp_users` SET `user_pass` = MD5('PASSWORD') WHERE `wp_users`.`user_login` = 'admin' LIMIT 1;

After you login on your WordPress installation, it will upgrade your password to the new phpass hashing.