Hi,
I stole this from wikiAnswers, hope it helps!!
The easiest way is to heat it and here's how.
Lay a paper towel over the hardened wax. Place a hot iron on top and move it over the paper towel. The heat will melt the wax and the paper towel will absorb it. Repeat as necessary until all the wax is gone.
You can keep using the same paper towel over and over, but if it gets too full of wax, grab a fresh one.
This method also works on wax spills on carpeting, tablecloths, counters, etc.
Alternatively, you could freeze the wax on your fireplace surround using ice cubes, then chip it off since the marble shouldn't scratch but the heat method is faster and easier with less mess.