You should be able to delete/uninstall the older versions, as long as they are in seprate folders. Just make sure when it shows you the directory it is removing; that it is the right one. And avoid removing shared files (that other programs, ie, your other UO folder, would both use). It should prompt you that you are removing a shared file.
Is there a reason you are removing them though? .. I've never had to remove one - it's always installed over the other one (if I remember correctly)