Remove the screw at the upper right corner. (Picture 1)

Carefully work the ribbon circuit, pictured at the left side, back and forth to free it from the plastic retainer. (Picture 1)

Lift the black locking mechanism up (Picture 2) and gently pull the ribbon circuit to detach.

Upon completion of this step, the lower circuit board should be attached in one place and be freely hanging as shown. (Picture 2)