Certainly you can do a change of address. Just prepare a letter to the OCP with your old address and New address, and go complete the form c4-1.

Check the list of charges for your permit type,but EU is from CHF

http://www.ge.ch/etrangers-confederes/fr/?rubrique=emoluments

link is and I think you must go to there address or pay by trasnfer and send a copy of proof of the payment

http://www.ge.ch/etrangers-confederes/fr/doc/c4-1-changement-adresse.pdf

ADRESSES / HORAIRES
Service Étrangers et Confédérés
Route de Chancy 88 - 1213 Onex
Ouvert les jours ouvrables du lundi au vendredi, de 7h30 à 15h.30 sans interruption.
Internet : www.ge.ch/etrangers-confederes

COORDONNEES BANCAIRES
Banque bénéficiaire : Banque Cantonale de Genève / CCP 12-1-2 Clearing : 788
Compte courant : Z 3285.51.32 (IBAN : CH21 0078 8000 Z328 5513 2
Rubrique : Office cantonal de la population / SEC Code SWIFT : BCGECHGGXXX)
Motif versement : Nom, Prénom, Date de naissance de la personne concernée et Type de prestation payée

this is more useful info.

http://www.ge.ch/etrangers-confederes/fr/sejour/welcome.asp?rubrique=changement-adresse

if you dont understand, use the bing translator

http://www.microsofttranslator.com/

Hi,

could you give me the exact webpage where I can see how much I have to pay for the address change??? Thank you! 

It's all here:

http://www.ge.ch/etrangers-confederes/fr/?rubrique=emoluments