It folds. For ease, lower the roof and windows. Look just below frame on outside of rear seat area, you will see 2 holes on each side which correspond to pins on your deflector. The longitudinal hinge goes forward.
Unfold deflector but do not let it lock into place completely flat yet. Locked it by mistake? Gently bend it in the middle to allow it to be in a slightly "hinged" position. Place the 2 pins in the holes on one side. Place the other two pins into the other side whilst allowing the deflector to snap into flat position.
Gently lift the hinged piece upwards till it snaps into position.
Apply gorgeous woman to front passenger seat and belt into place (OK - a man will do if you are so inclined). Get into driver's seat. Raise the windows for most aerodynamic effect. Find a place to drive like a bat out of hell and smile like a wicked politician whilst enjoying the wind which will not much tousle your hair, nor your passenger's.
To remove, reverse the process. You will find that the deflector in up position is also an excellent HID diffuser at night. Be somewhat gentle about folding the upright down, less so about folding the entire unit upward to remove it.