From the View Contact Screen, click on the icon and then click on the icon next to the site you wish to modify. Then, click on the Delete Button at the bottom of the screen.
Overview
As long as you have Delete Security Rights, you can delete a web site.
If you delete the primary site and there is another site on the list, the first site next on the list will be assigned primary.
See Also
Modifying The Address On An Existing Site