soap works any cheap soap chip it off in larger pieces
Loose paint will need to be scraped off. If it isn't peeling, you can use a paint stripper to remove it. Either is messy, so protect your floor.
If they are Plaster walls, you would be better off to scrap loose paint and wash with TSP rather than striping. The paint will be bonded to the plaster.
You could go right over the paint with the plaster then sand and paint