Anyways, there are two different versions of the type-5 mouse. Lord only knows what they were thinking at the time. Remove the mouse ball. Disassemble the mouse by removing the 3 bottom screws and remove the top cover. Unplug the circuit board from the cable and flip the board over.
Installation is the reverse of removal.
Remove the felt pads on the bottom, exposing the screws and plastic tabs at the top. Remove the screws and pop the tabs out using a flat-bladed screwdriver. Remove the top cover. Reassemble, being careful to get the flex-cable back in all the way without breaking it. Also make sure to route the main cable that runs out of the mouse correctly, if you don't lay it in the proper channel then you can cause binding of the middle button.