Remove the 7 screws from the back cover with a Phillips #0 screwdriver

Once all 7 screws have been removed, you can start to pry apart the back cover with your fingers/nails or use a plastic opening tool and carefully start to seprate the back cover from the main chromebook. See pic

When prying the bottom cover away from the main chassis, you can follow the order of the colored arrows starting with the red arrows while working your way around to green and so on. However, this order is not mandatory but seems to be the easiest.