2 or 3 scews on the inside and a bit of a wriggle and off it all comes, just have to jiggle about to get the new bits to line up, at least i think thats right, the caravansplus site is the place for the instructions and to buy one.
The little spring was the only that can bring you unstuck, it wont fling out but its tiny and needs to positioned a particular way. Youtube and @G Daddy's PDF should show that