I presume, that you want to delete URLs in the dropdown menu
of the address bar.
In KM 1.0 you can delete all of them by going in
the menu to Tools/Privacy/Clear URL bar history.
To delete only some of them, you can delete the
concerned lines in prefs.js, for example
user_pref("kmeleon.MRU.URL5", "
http://kmeleon.sourceforge.net/"
after having closed the browser.
The URL in the dropdown menu would be gone after
restarting the browser.
prefs.js is in your Profile.
The location of your profile can be found in
Edit/Preferences/General.
Fred