Looking at a picture of a replacement head, I noticed that it is just a "popper".
http://www.voltexdesign.com/images/articles/tete-tizio.jpg
If you insert a screw deliver with a wide (about 5mm) blade next to the head itself, between it and the plastic "grommet", it magically pops off. Just be careful.
If you plan to replace, pop it back on and off again to give you confidence that it is an easy thing to do.
Michael Kenward, December 2010