First, unplug all the connectors from the box.

The box is held onto the frame with 4 hex head screws. Remove those and it should come off.

Mark the wires and where they go on the board, if you are unsure the purpose of a wire, refer to the RAMBO wiring charts available at Rambo - RepRap

We will need the switches, connectors and wires for the rebuild, save those. When you have an empty metal box, you are done.