Remove the three Phillips screws in the battery compartment near the latch. Apple was nice enough to tilt these screws at a slight angle to make them easier to remove.
Do not yank the upper case off quickly. The case is attached to the logic board via a ribbon cable.
Lift up the back of the case and work your fingers along the sides, freeing the case as you go. Once you have freed the sides, you may need to rock the case up and down to free the front of the upper case.
Peel up the two black protective sheaths on the bottom of the keyboard. It is not necessary to fully remove these, but only to peel them back enough to access the screws beneath.
There are four locking tabs along the back edge of the keyboard holding it in place. These tabs must be straightened before you can remove the keyboard.
The keyboard on A1261 models has five locking tabs. Their locations are shown in the second picture.
Place the upper casing on its edge and use a spudger to push the keyboard away from the casing, poking the spudger through the central keyboard screw hole. Grasp the keyboard as it separates from the casing.