How to change the buckets on a jcb 803 digger?

I can't change the buckets / heads on a jcb 803 mini digger. The pin and small bolt comes out but nothing moves. I have tried lifting the bucket and shaking it but no movement. Its on hire. I knwo it comes out because the guy that delievered it managed...

Any suggestions, or ways to get hold of a user manual or online video?

Kate, February 2009