Temporarily unplug the router that DreamScreen is originally connected to, and then power cycle the DreamScreen hub - this will cause DreamScreen to display its "DreamScreen1234" and wait to be connected to the new network.
I am not sure I understand your last statement correctly. But the Factory Reset feature does indeed reset all Settings back to Default.
To set the number of LEDs you have installed, go to Settings > Installation Settings. There you can select Classic, Mega, Xtreme, or DIY. If you installed a set of DIY LEDs, then the DIY setting allows you to configure the quantity of LEDs installed and their orientation.