Start disassembling the headphones by removing the ear cups. Use a plastic sprudger to pry up the cups. Do your best to not snap off any of the clips

Remove the screws that hold the driver component

Remove these clips that secure the headband studs

Now the headband can be fully removed. Note that this picture is a reconstruction, and shows the wire already removed from the headband.

You'll need to desolder the wire from the left-hand driver in order to remove it from the headband. I recommend taking a photo so you know the polarity of the wires.

Next, start the assembly of the new headband.

First, seat the nuts in the nutholders

Install the washers onto the studs

Install the endcaps, studs and nutholders into the headphone case

Next, clip the new headband onto the studs

Replace the drivers and ear cups, then repeat for the other side. The wire will be loose at this point, so  you might want to tape it up. Or, you can wrap the whole headband with fabric tape, or just use an off-the-shelf headband cover. Done!