Use a flat head screwdriver under the tab to remove the top from the bottom.

Once the top has been removed, move the fan out of the way to expose the wiring and circuit board.

Note the relative location of the fan. To align the fan again during reassembly, it may be beneficial to have the vent for the fan off and use your hands to align the fan with the four holes. Use two of the screws removed in the previous in opposite corners to ensure the fan is properly aligned.