First remove the back part of the wii remote and the batteries. Then use the tri wing screw to unscrew the four small screws.

Next use a flathead screwdriver or maybe even your finger nails to pry apart the two pieces. There is a clip on either side of the d-pad which require the base piece to be squeezed inwards.

BE CAREFUL TAKING THE TWO PIECES APART! IF NOT DONE CAREFULLY YOU MIGHT END UP WITH ALL THE INNER PIECES FLYING EVERYWHERE!