You can delete custom MIME types at any time. However, you can not delete system-wide MIME types - please contact your hosting administrator if you have a problem with one of these.
To delete a MIME type:
Click on the MIME Types button on the home page.
A list of customized MIME types is displayed underneath the User Defined MIME Types area. Enter the details of one of these in the MIME Type and Extension(s) fields.
Click on the Delete button.