There are many cases where the default list of allowable file types are too restrictive for the needs on a website. For example, if you are using the Media Module, you might want to be able to upload MP3 files to play on your site. If you look at the default list of allowable files in the most recent version of DNN, this type of file cannot be uploaded.

swf, jpg, jpeg, jpe, gif, bmp, png, doc, docx, xls, xlsx, ppt, pptx, pdf, txt, xml, xsl, xsd, css, zip, template, htmtemplate, avi, mpg

In order to manage this list, you will need to perform the following steps:

1. Login as a Superuser (or Host)
2. Go to the Host Settings page
3. Scroll to the bottom of the page, in the Advanced Settings > Other Settings section
4. Find the "Allowable File Extensions" field
5. Add or remove file extensions as desired to allow or disallow file types, separated by commas
6. Click "Update" at the bottom of the page to save your changes
   

PLEASE NOTE: Adding a file type to this setting can potentially open your website up to very significant security risks. Ensure that you allow the minimum number of file types, and only those that are absolutely necessary.