The process of making your domain a Class B is quite simple. All you need to do is create or modify a file called .htaccess located in the root directory of your site and add the following lines, changing the red text to match your domain.
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.domain\.com$ [NC]
RewriteRule ^(.*)$ http://domain.com/$1 [R=301,L]
Taken from this site
www. is deprecated.