It looks like they're plastic (assuming it's the white clips you're talking about?) a hairdryer on them to warm them should make them less brittle and easier to remove.
I googled this not so long back. Found info on pinside.
I think the jist of it is you have to cut the clips off as you run the risk of snapping the post.
Try using a good pair of side cutters.
Post how you get on as I’ve got to attempt this soon, good luck