First remove the AirPort antenna (the larger of the two), located near the power button.

Slightly squeeze the two retaining arms toward each other and lift the AirPort antenna off its post.

Squeezing the two posts excessively will surely break them off the internal frame. Work delicately.

During reinstallation, you will have to slightly squeeze the two posts together so they fit into the openings on the AirPort antenna board.