This is a very common question here. Do a search on the top and some very good answers will show up, A good scrubbing will lighten the color, but it is doubtful if you will get it all off.
The bigger issue is why? Soot on the front of a brick fireplace is an indication that the design of the fireplace is faulty. This should be looked at by a pro to determine if there is anything that can be done to correct this issue. It can be as simple as installing a good quality door front, a new smoke shelf, to complex as raising the chimney so it draws better.
I remember seeing them use foaming Scrubbing Bubbles and a brush then rinsing, on staging and home improvement shows.
TSP,Tri-sodium phosphate found in any hardware store.
Puff baking soda &spray vinegar, dab dry