It is held on with double sided tape, 2 rows. Top is taped down and so is the face. Get a utility knife, with a brand new sharp blade. Run the blade into the crack/space along the top from the bed side (v. bumper side) of the gate. Pull it all the way across the gate length (leave the gate closed the entire time of this process). Then, pull the top back with your fingers and run another cut.
When the top is free, bend the spoiler all the way back to the point where you can see the tape that is holding the face of the spoiler to the gate and do the same thing there. The spoiler will not deform so you needn't worry about that.