Your first step would be to unscrew all all screws on the back and take the case off. You take the case off by placing a spudger on the line edges , and then place it inward, forcing it to separate the two parts.

You first remove the gabbles by gently pulling them and do the same for the WI-FI board

You take the mother board off by flipping the upside-down and the screen should pop right off.

Unscrew and gently slide wires through frame

The DS should look like this and to put the DS back together simply follow steps back wards.