I presume you are talking about the caps on the wheel nuts.
You don't need to remove 4 of them, the wheel brace should fit snugly over them. The one with a dimple in it is the only one which comes off, there should be a plastic sleeve in the wheel well in the boot which fits over the dimpled one to pull it off. Then there will be a security nut under this, the attachment for which should be in the boot with the plastic sleeve, maybe its in the gloove box.