if you want the bumps gone, then you do have two options, sanding and sanding allot or re floating the walls. One is just about as easy as the other.
I would first after sanding use a good primer like Zinzer BIN and coat it good. then apply your finish coat.
You could try one of those painters draw type knifes that use a sharp blade and you pull down to strip off lose paint. This tool could remove the top of those bumps for you. The tool comes in one inch and two and a half inch blade. Just with one hand push down on the work and the other drags along the wall sides and strips the paint, in your case textured bumps.