You could use a power washer, paint thinner, sand blast it. All stuff you can rent or purchase somewhere or have done.
You have to put a layer on it because you can't get it off. Just paint over it the same colour your concrete is!
Wow -Some very good info so far ( not ) . Go buy you a can of oops paint remover. Most hardware stores or paint stores have this. What I do not remember is if it removes all types of paint (READ CAN). Give GOO GONE a try. Or just use a good paint scraper along with some very corse sand paper, if you are unable to find an easy way out of this. And any time you paint, protect the surounding stuff with blue masking tape and paper or plastic or a drop cloth. AND STOP SHOPPING AT WAL-MART. HAPPY PAINTING OR UNPAINTING IN YOUR CASE__GOOD LUCK__.
Just put more concrete on it.