However if you delete some default skins such as teak zeppelin.asws and silver panel.asws, they'll come back when you do an update.
To remove default skins go to Add/Remove programs applet into Control Panel click on the 'Change' buttom and uncheck skins.
This doesn't remove ability to use skins, but should stop default ones comming back.
Silver Panel cannot be deleted (so does Low Res but this one is not shown on the list)
The other 2 default skins, Teak Zeppelin and SZC-KDE can be removed.