Group the ezPosters.
Set all the ezPosters to the same network. You can use WIFI router or the WIFI hotspot designed in the ezPoster to connect all the ezPoters to the same network.
In the software, all the devices under this network will show up in the device list
Then select the ezPosters and use group wizard to form a group.
After the group is formed, content uploaded to this group will be done to each of the ezPoster within the group.