The property change of a domain is an operarion thar requires payment ( € 7,00 + vat). To buy it you have to login the control panel click on "Active domains management" > "Panel". From here it's possible to change all the data of the accountholder.
(Click on the images to zoom)
The updating of contact data (address, telephone number, email etc.) it's free.
For .EU domains it's possible ti change/update only the registrant data.