Use the flat end of a spudger to lift the I/O board connector up and out of its socket on the logic board
Be sure to lift straight up on the connector as you disconnect it from its socket. The socket is very deep on the logic board and prying it from side to side may damage the logic board
Gently push the tip of a spudger under the black plastic flap stuck to the display data cable lock to make the lock pop upward and away from the socket.
Remove the small rubber gasket from the corner of the upper case near the display data cable.
If the heat sink seems to be stuck to the logic board after removing all four screws, use a spudger to carefully separate the heat sink from the faces of the CPU and GPU.
Remove the heat sink from the logic board.
Logic board remains.
When reinstalling the heat sink, be sure to apply a new layer of thermal paste. If you have never applied thermal paste before, we have a guide that makes it easy.