I assume you are referring to the top idlers. There is no secret to it. Take the skid out and get a drift of some sort (chiesel, punch, flat bar) and drive them off. Try to keep it on the bearing race and you can save them. You can make up a puller, but it has to close in tight to the bearing or you will just wreck the wheel. They are pressed on. If you were one of the lucky ones you may have the bearing retaining clip on the inside and you can take that off then slide the wheel off and then have just the bearing to get off.