Begin disassembly by removing the battery

Peel off the sticker underneath the battery to reveal the small Philips screw underneath. As my particular mouse had already been disassembled, the sticker is not shown in the images

Using a flat blade screwdriver or similar instrument, peel off the rubber pad at the upper edge of the mouse to reveal two more screws

Unscrew a total of 5 Phillips head scews as marked