Unscrew the four screws that hold the bottom panel using the Phillips 02 screwdriver.

The screws will not come out of the bottom panel. They were designed to become loose but not be removed. This prevents you from losing them, and prevents the Roomba from sucking them up if they came out during cleaning.

Once you are sure that all the screws have been loosened as much as possible, then lift the bottom panel up off the Roomba.