Solved
Thanks for your answer. I knew I could do that but the manual says that using the remove menu item will also remove all other files associated with the VM. (For this very reason software is being sold for money that removes Mac programs, completely!)
The problem and solution lay in this that I had Parallels set to auto load my Windows VM. When I disabled this option, remove became available again.
I understand that remove would be greyed out for the VM that is loading but it would seem logical to me that theother VMs could be removed. No? John