How do I remove paint ridges from an interior wall?

I painted a castle on my sons bedroom and now am re-decorating. The lines from the bricks on the walls show through if I paint over them. A razor scraper doesn't take off the ridges, and sanding it does nothing either. How do I remove the ridges to repaint?How do I remove paint ridges from an interior wall?
It depends on how deep the ridges are. When I do prep work and I'm dealing with ridges on a wall, If the ridges are high, I try to sand them down and/or scrap them as smooth as possible with a 5in1. Then go over the ridges with two skim coats of drywall mud, sanding lightly between coats with a sanding block. When the ridges are low, I just skim coat them with drywall mud. Another thing you can try is to cut out the top outer layer of drywall with a utility knife and peel it back or scrap off the paper with a mud knife, then prime with a stain blocker and put a couple of skim coats of drywall compound over it. Sand and prime after wards.