I have bought this non-genuine earpad replacement in Media Markt (Vienna) - PUNEX Ersatz Schaumkissen. The size (big) I estimated in the shop and it seems sufficient.
0. Motivation. For comparison - old and the replaced new one:
1. I took the old earpad off. You can see the gap around the earpad. I didn't want to dismantle it further.
2. Just with my bear hand I put a new earpad on the headphone.
3. But then it looked like this. The earpad didn't fit tightly.
4. So my trick was to use some sharp and very thin knife. I pressed carefully the edge of the earpad inside the gap all around the headphone.
And that's that. Happy listening.