How to change right speaker on ACD?

Left and right are usually referenced when the device is in its operating state. So when you are looking at the monitor straight on, the right speaker is on the right (the same side as the clock in your dock), and the left is on the left (by the apple menu of your dock)

There isn't a tear down on iFixit, but the Apple service guide is linked on their system.

Its not as detailed as the iFixit guides are, but you will be able to fully trip it down following the guide if you scroll about 2/3 of the way through the document. it shows you have to remove specific parts.

Its the document that Apple distributes to its repair centres, so it is pretty comprehensive.

Its found here: led_cinema_display_24.pdf

But in essence, you'll need to remove the glass panel with a suction cup (carefully to prevent damage to the alignment pegs that are on the underside of the glass), then unscrew the LCD panel (torx screw on left and right side), then lean it forward to disconnect the LVDS cable and the backlight cable from the main logic board.

Once that is disconnected, you will see the speakers and their connection cables clearly and will be able to trace them to their ports and disconnect them.

I hope this helps.