If you have a viscous clutch fan, you need to remove the fan. This is done with two long thin wrenches. One for the hub nut (~36mm?) and a spanner for the nuts on the end of the pulley. I got mine from zdmak.com (ebay) but maybe PeachParts has them as well. Once the fan is off the end of the shaft you can lift it out and then remove the shroud.
I see you are in France so here's what they look like -
http://zdmak.com/wbstore/main.asp?action=PROD&PROD=M86-36WR&CTMP=1