First we need to remove the earpad. It's attached to the piece with those little pins. Take care to not break them. You can see this pins if you lift the cushion upwards. You can then use a thin plastic tool to get the plain layer of cardboard out of those pins.

This can be done with just enough force to bend the cardboard base without damaging the plastic pins.

After removing the 4 philips screws the under side will be unlocked.