Using a screw driver, gently release the two grey plastic clips inside the battery compartment in order to remove the right part of the upper case.
There are two more grey plastic clips holding the left part of the upper case. They are not easy to release as they are hidden from view prior to disassembly. They are in the same position as the two in the battery compartment, but on the opposite side of the trackpad. Try to stick a flat pry tool into the clip holes and push the clips inward (toward to screen) so they disengage and release the left part of the upper case.
Lift the upper case off the computer.