1. Install UrlRewrite extension

iis.net/download/urlrewrite

2. Edit Web.config
<system.webServer>
<rewrite>
<rules>
<rule name="CanonicalHostNameRule1">
<match url="(.*)" />
<conditions>
<add input="{HTTP_HOST}" pattern="^yourdomain\.com$" negate="true" />
</conditions>
<action type="Redirect" url="http://yourdomain.com/{R:1}" />
</rule>
</rules>
</rewrite>
</system.webServer>

http://stackoverflow.com/questions/4882508/how-to-remove-the-www-prefix-in-asp-net-mvc