Actually, there is no way to convert lumens to candlepower. You are talking about two very different measures, illuminance vs. luminance (apples vs. oranges).
Lumen - energy of 1/683 joules per second, measured at a wavelength of 555 nanometers.
Candela (candlepower) - lumens per steradian. (A steradian is a solid angle subtending an area of R squared at distance R from the apex.)
Simplified, a lumen is the measure of the total light output of the light source (this is the luminance (radiance) of the light source.)
Candlepower is measuring the brightest spot of a beam and is reflector dependant. If you take a Mag flashlight, just by focusing the width of the beam, you can adjust the "candlepower." The luminous intensity stays the same.
For those physicists out there that are going to correct me on the convertible relationship, I know. I understand the inverse-square law, etc., but that doesn't apply for all practical purposes to this discussion.