1.Open PHPMyAdmin and goto sql editor and check root user password by using
SELECT user, host,PASSWORD FROM mysql.user;
2. Run the following sql command to change the password
SET PASSWORD FOR ‘root’@’localhost’ = PASSWORD(‘newpwd’);
3. Changing the root password will create issue with PHPMyAdmin as it is by default configured to run with root and blank password. Reset it to new password in \wamp\apps\phpmyadmin3.3.9\config.inc.php file
Refer http://dev.mysql.com/doc/refman/5.0/en/default-privileges.html for more details about all OS environments.