Ok with these new sets some may want to use the walls as a freestanding piece and not use it as a storage or mobil set .
First get a small slotted screwdriver .
With your hand holding the set use the screwdriver to pop out the corner tabs . Keep holding pressure on the backing plate to not allow the tabs to snap back in .
with the screwdriver gently pry the upper center tab out and the rear plate will release
The backing plate has the two tabs on the upper corner and the one in the upper middle and the two bottom tabs that act like a hinge when the uppers are released
Note : the 4776 was a bit harder do to the configuration of the set . On the 4775 I was able to do it with out a screw driver and simply grasp the handle w/ one hand and spread the upper corner out w/ the other and twist the back off . ( it has been over 100 degrees here so the plastic is warm )