I update my kernel of Debian from 3.x to 4.x.  

Docker storage become overlay2.

```
ls /var/lib/docker/ 
containers  image  network  overlay2  plugins  swarm  tmp  trust  volumes

```

old directory structure is 

```
aufs  containers  graph  image  init  linkgraph.db  network  plugins  repositories-aufs  swarm  tmp  tmp-old  trust  volumes

```

My images is in aufs directory, I can not start docker service with old directory. how can I move my images to overlay2?