It is very easy to transfer a virtual machine (hereinafter VM) to another disk (memo).
The VM must be stopped.
In the directory / etc / libvirt / qemu / we find the hml we need, let's say vm01.xml VM and open it with your favorite editor.
Look for the <source file = tag and change the "current location" to "new", save.
Now we move vm01.img to a new location in any way available to you.
We need to inform about our changes KVM / Connect, for this we write in the command line.
$ virsh --connect qemu:///system
virsh # define /etc/libvirt/qemu/vm01.xml
All VMs can be started.
Something like this.