[Zope] upgrading a product

An upgrade to KM|netNews was just released. Everytime I try to import the file, it says "already exists". Simply renaming the current product does not help as I then get "Permission Manage... already exists". I tried renaming those files, but was told that operation could not be performed on these file types. Could someone please be explicit about how to upgrade an existing product in newbie terms? Thanks in advance, Liz Pelletier