Unscrew the four Phillips screws along the top of the back cover.

The screws are held in place by locking washers, and will not come out of the back cover.

Hold the device in one hand and turn it over.

Grab the top edge of the back cover with your opposite hand so that the cover does not fall back into place.

Flip the 3DS over again so that the back cover is facing up.

Pull the back cover up and away from the rest of the device to remove it.

Insert a plastic opening tool into the notch in the lower case above the battery.

Pry the battery up with the plastic opening tool.

Grab the top edge of the battery and lift it out of the lower case.

Remove the nine 6.3 mm black Phillips screws from the lower case.

Remove the 2.4 mm silver Phillips screw above the game cartridge slot.

Lift the bottom edge of the lower case off the rest of the 3DS.

There are still two ribbon cables connecting the mother board to the case, so be sure not to pull the lower case all the way off.

Use a plastic opening tool to pry the shoulder button ribbon cables off their sockets on the motherboard.

Remove the lower case from the device.