Maybe I'm not too good at searching for answers but I found all kinds of creative and destructive ways to move the files.
The most common I found is to remove your VMs from the manager without deleting the files. "Remove the VMs from the manager without deleting the files. You can then move the entire VM folder (not just the bare VDIs) to a new location, before adding them back to the manager."
Here's how I did it... Use these instructions at your own risks

- Shutdown the manager
- Copy the directories under Virtualbox VMs where you want them (full directory - logs, *.vdi, *.vbox*, etc...)
- Locate .Virtualbox folder (mine was in c:\users\[username]\.VirtualBox
- Backup VirtualBox.xml and VirtualBox.xml-prev
- Edit VirtualBox.xml with your favorite editor (or wordpad)
- Locate <MachineRegistry>
- Change the SRC location to the new one...
before <MachineEntry uuid="{afbc1273-1d06-4f6c-9068-e5c044eb4975}" src=" C:\Users\[username]\Virtualbox VMs\XP SP3\XP SP3.vbox"/>
after <MachineEntry uuid="{afbc1273-1d06-4f6c-9068-e5c044eb4975}" src="E:\VirtualBox VMs\XP SP3\XP SP3.vbox"/>
- Save
- Remove files from original location eg C:\Users\[username]\Virtualbox VMs\XP SP3\
Now ready to go to run your VMs from the enw location.
Bingo.