There are a few ways this can be acheived depending on what you want the end result to look like.
the best way to remove paint from a concrete surface and not cause serious damage to the substrate would be to chemicaly remove it. do a search in your area for prosoco products.
now you have to keep in mind that these paint strippers are very industrial and if mishandled can cuase damage to the suroundings well as yourself.
if you decide to go this route get a pressure washer, wet suit, heavy duty chemical resistant gloves, a face sheild and rubber boots, hide the wife, kids and pets.
these strippers can litterly burn/melt your skin off, so be carefull. apply as per manafactures specs, rinse off with low pressure. when you are satisfied with the rinse down, powerwash off and repeat these steps. finanly since most of these stripper are a very high akline product (i think 12-13 on the scale) you will need to neutralize the surface. prosoco sells a concrete cleaner that is acidic base and shoud work.
chemical stripping of paint is or has got to be the most sloppiest jobs i have ever done, the paint litterly melts and gets on everything.
other ways are to sandblast, but this will make the concrete more porous and prone to future water damage.
soda blasting is another option and will not harm your surface as much as sandblasting will. the city of chicago uses this technique to remove graffiti.
you can sandblast or grind off the paint and hire companys that will refinish the concrete. they can make it look it brick or a stone.
you can alwasy morter and tile the walls.
last option would be to again remove the paint via sandblasting or a grinder and add a layer of culture stone or brick over it to make it more appealing.