Pretty sure it’s just a strong adhesive. When I pulled the ones off my Sierra I used a knife to get it between the fender and the flare to cut it. That said, the fenders were getting thrown away so I didn’t care about scratching them. If you are putting new ones on you could do the same, just being careful to keep the blade down low where the scratches will get covered by the new flares. If you aren’t putting any back on, it would look pretty terrible. Not sure how to handle that.