Double-check that the SIM tray is removed before taking out the motherboard.

Use the flat end of a spudger to lift the top edge of the motherboard up until you can grip it with your fingers.

Remove the motherboard.

During reassembly:

Make sure the eight cables that connect to the motherboard are out of the way so they don't get stuck under the board.

Lay the motherboard in its recess and press down to secure it.