There is a slot on the wall of the battery compartment that locks the lower case in place. Use a small flathead screwdriver to pry out the slot's lower rim and pull up on the lower case to free the slot from the tabs holding it.
Run a spudger along the seam between the lower case and upper case on the front of the computer to free the tabs locking the lower case. Pull up on the lower case and continue to use the spudger as necessary until you hear three distinct clicks.
There are three tabs over the optical drive that must be released before the lower case can come off. Slide the spudger into the lower case above the optical drive and run it toward the back of the computer until you hear three distinct clicks.
Before you can yank the upper case off, you must disconnect the trackpad connector, the blue and white power cable, and speaker cable as described in the next steps.
Lift the upper case from the right side and use a spudger or your finger to disconnect the trackpad connector hidden beneath the white plastic tab. Due to model variatons your trackpad connector may be different from the one pictured.
The connectors at the ends of the cables are attached very firmly to the sockets on the logic board. Pulling directly on the cable will either separate the cable from its connector or the socket from the logic board.
Lift the upper case enough to disconnect the blue and white power cable from the logic board. Using your fingernails or a dental pick, carefully pry the connector from its socket. Make sure you're pulling only on the connector and not on the socket.
Lift the upper case off completely and disconnect the multicolored speaker cable from the logic board. As before, make sure you're pulling only on the connector and not on the socket.
Tip: the multi-coloured cable may be easier and less daunting to disconnect after removing the top heat shield. Prop the top case upright while removing the shield - the connector is then much more accessible.