Use your fingernail or the flat edge of a spudger to carefully flip up the upper LCD ribbon cable retaining flap.

Make sure you are flipping up the retaining flap, not the socket itself.

Pull the motherboard away from the DS Lite to separate the upper LCD ribbon cable from its socket on the motherboard.

Remove the motherboard from the DS Lite.

Now you may open the retaining flap for the lower LCD screen in the same way and separate the lower LCD screen from the motherboard.