Mime type is not getting updated

I have Windows Server 2008 R2, so I must be running IIS 7.5. I am trying to change the default mime type associated with an extension. Fot that I changed the global mime map and also added the <staticContent><mimeMap> section to web.config.

However, when the browser downloads my file, I see that the http header still has the old mime type.

Am I missing anything? What is the correct way to change the mime type of a file?

Apeksha