How to make the basement wall smooth (concrete), 40 year old home. There's some humps formed by the concrete or paint

If it is buckling due to foundation problems then it needs more than smoothing. Are you sure it isn't that?

Remove the humps and see if they are calcium build-up,water doing damage and buckling the joints.. etc

To smooth,you'll need to take those out,find out why they were caused and replacement with the correct type of filler.

Let us know what you find out and we'll see to the remedy.

If its just wavyness and bumps from forming you have 2 choices: build up or grind down. Grinding a concrte wall and getting it flat can be difficult. You could try parging the concrete but both will be patchy. Are you converting this to a living space?