How do i remove wheel hub from my rapide roller trailer?

Hi,

I need to service my wheels on my Rapide Poller 11 trailer as one of them keeps sticking. The wheel is off however I am having troble removing the hub. I cant seem to remove the dust or hub cap ( it may be sealed i dont know). From the rear is a large nut which had a cap on it and seems to be holding the whole thing together and is attached to the suspension arm(is this the nut that need undoing?). At the rear of the hub there is a pin with a split pin through it, I have no idea what this is. I dont want to start stripping the thing down in case the whole thing falls apart as I need the trailer to pull out a boat. Any help would be appreciated.

Thanks