After the computer base (#1) is facing up, use a Philips screwdriver to remove the two captive screws (#2) which hold the base panel (#3) down.

Then, use a spudger (#4) to lift up the panel. You can also use your fingernail to lift it as well.

After the front has been lifted up a bit, the non-screw side of the panel will need to be slid forward a little to finish lifting out the base panel from the computer.