These parts are on a tapered shaft, meaning that they are designed to wedge themselve on when you do up the bolt. You will need to use a splitter to get them off. There is a couple of different types, one looks like a forked wedge, another a bit like a clamp with a forked end. Don't try doing it without the right equipment, you will only break something and it will cost you more money. Go to a suspension shop or your mechanic and get him to split them for you.