Onec you disconnect the battery now use iFixit Precision Bit Driver and iFixit Precision 4 mm Screwdriver Oval Drive Bit (0.5). Place the Screwdriver in the top of screw and rotate it clock wise until the screw comes out.

Remember to use magnetic mat to keep those tiny screw safe so that you will not lose it. Repeat the steps and unscrew all the screw.