You can redirect all of the requests for yourdomain.com domain to www.yourdomain.com by modifying your website's .htaccess file. You need to add the following lines at the beginning of the file in order to setup that redirection:
Where yourdomain.com is your actual domain name.
RewriteEngine on
RewriteCond %{HTTP_HOST} ^yourdomain.com [NC]
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [L,R=301]
Where yourdomain.com is your actual domain name.
