The KAC-501, 502, 503, and 504 modules can be added and removed to the KMD-540 display unit very easily. Labeled screws are removed from the side panel and the panel is slid back. A screw on the top for the locking bar is removed, the bar is turned 90 degrees counter-clockwise and then pulled up through the top of the unit. For detailed instructions, please view this page from the KMD-550/850 Installation Manual.