Zope Management Interface, I presume. Is this in the Products folder of the Control Panel? Yes. Delete, what is likely the "open box", zClass product in the Products folder.
, which should make it dissapear in your product selection menu. They don't appear in the *Select type to add...* pull-down, if that's what you mean. Yes again. This is where a valid zClass should appear, so we might be talking something other than a zClass. Maybe a sub-class?? or you have a mangled zClass.
But all the old instances will exist. Delete them manually. OR Globaly, search on the meta-type and delete. How should I do this? I have root access. If you have many then you need to write a script. Otherwise just delete them like you would anything in the ZMI. Actually I havent had to do major clean-ups yet in Zope. But my guess is you need to use TransparentFolders to look into all your sub-folders from the root, to locate all the instances of your zClass by searching for the meta-type. something like productValues('zclass-meta-type-name-here') You will have to delete programmatically. OR use the FIND tab.
I dont think it matters, but I would delete the instances before your delete the zClass. -Trevor