To remove the buttons section, you first need to remove the accessories below the buttons. See here for some useful information.

Pull the button section free and remove the grey front bezel.

You can now unplug all the connectors ensuring you note which ones are connected to which button. Once disconnected, the buttons simply push out of the frame.

To access the PCB, turn the button over and dismantle it by levering it where shown.

Take the PCB and begin your LED changes.