I assume your jockey wheel comes through the center of "A frame", as side clamp versions are self expanatory!!
Without a hoist or pit, you require to get the caravan, nose up as high as pos on the corner steadies.
Then with no weight on the wheel,wind down the wheel as far as it will go, loosening the clamp as you unwind.
The inner screw and outer tube will eventually seperate, so you can remove screw with wheel from bottom and tube with winder from top. Reverse operation for fitting replacement.
Cheers
Dave Mac