First power down the computer completely.

Next remove the battery by pushing in on the two sliding locks and pulling out.

There are 21 Philips head screws, including the four that were underneath the battery, as shown in the photo.

Remove the screws. Beware: Most are the same size, but a few may be different, depending on the exact model. On mine, there was a larger screw nearest the ethernet port, and two small screws nearest the middle of the battery compartment. Note the position of any differently sized ones.

Remove the plates covering the hard drive bay and the memory slots, and set them aside.

Pull out on the optical drive to remove it. Set it aside. Now remove the three small screws that were underneath the optical drive edge.

Remove the two screws that retain the hard drive caddy. To disengage it, slide the hard drive towards the edge where the optical drive was, and lift to remove it. Then set it aside.