The structure is held in place by 4 screws and some friction.

With the drives removed, peer inside to see the two screws at the bottom of the cage. Unscrew those. You might need an extender for these two.

Next, put the structure upside down and take off the 2 feet at the front of the cage (the side with the blue dot).

You'll find two screws under there, unscrew those too.