Flip your giant headphone over onto the "back" and unscrew the 4 Philips head screws with your PH2 screwdriver

Pry the plastic piece with the screwholes off the rest of the device, starting from the stem of the headphone.

Pull the tip of of the headphone off the the remaining stem piece. Now, the speaker can simply be pulled to separate the glue and remove it from this top plastic piece

Using your PH00 screwdriver, undo the single screw from the green circuit board. Lift the PCB out of the headphone shell.

Now disconnect the COLOUR-CODED connectors for the speaker and battery. these are the same connection type, so do not mix them up when reassembling it or you could seriously damage the device. red connector to red, white connector to white. In my case, the board connector slid right out with the cable, so use the image as reference to put them back