ok, thanks for your helpno, its not easy. You have to take the axle part way out of the carrier because there is a circlip holding the hub tight against the carrier and you can't just pull the sprocket hub off without first taking that circlip off.
Typically, a 36 tooth sprocket comes in two pieces (halves) so that you can put it on without taking the sprocket hub off in order to get the sprocket on.
I should say that it is simple work to do but a pain in the behind because it is a lot of work just to change a rear sprocket.[/b]