Delete a user-defined MIME type
To delete a MIME type, click the X icon under the Remove heading, and then click Yes to confirm that you wish to remove the MIME type.
You cannot delete MIME types from the System MIME Types table.
More about MIME types
For more information, read the Webmaster Toolkit list of MIME types.
You can also use your preferred search engine to research the MIME type that you wish to add.