On the server, there should be a wp-config.php file with lines near the top like
1. define('DB_NAME', 'putyourdbnamehere');
2. define('DB_USER', 'usernamehere');
3. define('DB_PASSWORD', 'yourpasswordhere');
4. define('DB_HOST', 'localhost');
[If those lines aren't in the file, look for a line like
include('/some/path/name/somefile.php') and find that file in your ftp files (it may not be in the WordPress directory).]
Lines 1-3 above give the database name, user name and password *for the database* that WordPress uses internally. You can use those to reset the password for the WordPress users.
If line #4 does say "localhost" then your database server is the same as your ftp server, and if you have shell access to the server, you can use the MySQL instructions in the article referenced above.
If line #4 doesn't say "localhost" it's likely you have phpMyAdmin access to that server and be able to follow those instructions to reset the password (and you don't need shell access).
But unless your "blog promoter" is actually hosting the site for you (i.e. he controls the actual machine where you files live) you may be able to contact the web services provider and get some help with the above from them. But if you're not sure how to use the admin area, you may need some additional help from someone who's familiar with installing and configuring WordPress.