There is one latch that stops you from pulling the upper case right off, located on the left side of the optical drive slit. To free the upper case, you will be pulling a thin metal latch toward you, freeing it from the clasp holding it in place.

Pry up the left side of the upper case slightly with your hand and wedge a spudger into the seam between the upper case and lower case.

Leave the tool in place applying pressure to the upper case for the next step.