You need an external (E10 I believe) torx socket to hold the stud while you loosen the collar bolt that is under the plastic cover. A closed end wrench (10 mm?) that has an angled head (so that it reaches inside the cavity) may be necessary. I have only tightened the collar nut, so I cannot tell you if there is something more difficult to get the pulley fully off.

I bought a set of E torx sockets at Pep Boys for $20. Nicer than the ones sold on Ebay at about the same price once shipping was factored in plus I didn't have to wait. You will want a good set of these for future repairs.

Please post your experiences taking this off. I will be interested to know if you were able to get the plastic cap back on that goes in the center of the pulley.