the fan is held on by a 32mm nut between the blades and the engine. You will need a long sturdy 32mm spanner. The nut is left hand thread so unscrews by turning to the right. I find the easiest way to undo them is to put the spanner onto the nut so that the spanner is vertical then hit the ring end of the directly downwards slightly towards the right (towards direction of release) with a hammer. Alternatively you could try and hold the pulley behind the fan nut on the 10mm bolts but this is much more difficult.