Fin Removal

Really stupid question time!!!
I've just sold my first custom painted board, and picked up another board in part payment, but can't remove the fins so i can paint this one!
How do I remove these fins (pic attached)? The plastic screw at the rear of each fin seems sprung-loaded in the rotational sense and I don't want to force them!
Any help would, as always be greatly appreciated
Clive
I've just sold my first custom painted board, and picked up another board in part payment, but can't remove the fins so i can paint this one!
How do I remove these fins (pic attached)? The plastic screw at the rear of each fin seems sprung-loaded in the rotational sense and I don't want to force them!
Any help would, as always be greatly appreciated
Clive