Rolling out updates
To update Virtlet to the newer or older version just change its image name/tag in DaemonSet definition:
kubectl -n kube-system edit ds virtlet
You should change it in four places there, for each container definition.
During the upgrade state of VM pods will change to
ContainerCreating but there is nothing to worry about. The VMs are still running. Kubelet just can't get the state of the VMs because Virtlet is not available during the update.
When Virtlet update is done you can check that the VMs are still running. Attach to
kubectl attach -it cirros-vm
Virtlet updates are done using standard DaemonSet update mechanism