Using your PH2 size screwdriver, remove the edge sweeping brush.

Using your PH2 size screwdriver, remove the 5 screws highlighted in the 2nd picture.

These top two screws highlighted in orange will unscrew completely if you keep going so be sure to stop unscrewing them as soon as you feel resistance.

Lift the bottom cover straight up off of the Roomba from the two spots the arrows are pointing to.