Question: I have a user (user1) that created a vm in virtual box install on the server.
I also have a user (user2) that created a vm in virtual box install on the server.
Now, I want to log in as admin and delete all virtual machines of all users.

the problem is that the vm is not recognaize when I am with admin since its in the user1 directory and user2.

Do I have a way to delete other users vms with admin?

Answer: 
Ok, after few more tests I found a way. Not sure its the best but it works.
While in admin login, I can run the command:
`vboxmanage register [Full path to xml file (vbox suffix) inside user1 vm directory]`
This will register the machine inside my admin virtualbox manager.
Then I can run the `unregister --delete` on the machine.
If `user1` and `user2` used the default settings of VirtualBox, the VMs will be stored in `C:\Users\%USERNAME%\VirtualBox VMs` (if you're using Windows at least). These could well only be the VM configuration files (the harddrives can be stored elsewhere).