As with any kind of textured surface there is rarely a simple answer. It depends, to a great extent, on how widespread the problem is. Small, localised issues are easy enough to resolve with a scraper or, sometimes, a heat gun. Larger areas can sometimes be tackled with a high pressure washer and/or physical scraping.
Blistering is usally indicative of trapped moisture so you will need to also ensure the wall gets time to thoroughly dry out before attempting to repaint.