Subfolder to Subdomain Redirection over IIS7

I have the latest version 3.9.1 installed on Windows Server / IIS 7 server “DiscountASPnet”.
Current situation: WP installed on http://www.domainname.com/blog
What I’m trying to do is to: use http://blog.domainname.com instead
Note: Current WP permalink configuration: post name “www.domainname.com/blog/sample-post/”