[wlug] Theme deletion...

Is it possible to delete appearance theme customisations (i.e. icons, controls, window border, etc.) that the user has installed manually (say, from www.gnome-look.org) but the Appearance applet refuses to delete? I've installed a number of themes/customisations that I can't delete because the 'Delete' button is greyed out. As a result I have a glut of entries to choose from, most of which I don't want any more. Sandy