To remove a device from a junction box, go to
Ribbon: DM Electrical->Devices-> 
Remove Device from Junction Box
Pulldown Menu: DM Electrical->Junction Boxes->Remove Device from Junction Box
You will be prompted to select the devices you want to remove.
Select objects:
All of the devices selected will be disconnected from the junction box to which they are connected. The loop between the device and the junction box will be removed.
If you want to connect a device to a different junction box, use the Add Device to Junction Box command. You do not need to use the Remove Device from Junction Box command to move a device from one junction box to another.