Painting curved staircase walls

The internal walls to my staircase are rendered with textures surface rather than smooth plastered. I would like to repaint them but wonder if there is a special technique for painting on render, or can a normal roller be used? Also I have 2.7m high ceilings and the staircase is curved which makes access to the upper walls problematical. My multi position platform type ladder will only let me reach so far. Any ideas how to reach the upper walls on a curving staircase please? Thanks Biko