Go to templates/tmpl_uni . Open _footer.html . Therf you would be able to find the string which shows the links to boonex. Don't remove the string which displays copyright. To change copyright text,go to settings in admin, search for 'copyright' string in language settings. Change it to what u want. There wud be two copyright strings. Edit both of them.
You can remove footer Boonex links only if you have got adfree dolphin license.