Remove the 4 Torx screws securing the Bottom Housing with a T15 Torxdriver.

CAUTION! On reassembly of the Bottom Housing, these Torx screws must be fastened securely. Tighten them FIRMLY but do not force them. This will ensure that the heat pipe for the CPU is in direct contact with the Upper Housing heat sink. On reassembly you will make an application of Thermal Paste to the heat pipe mating surfaces. This will become evident as you proceed through the next steps.