First remove the fire the outer brass part should lift off and there should be 4 screws.
How to remove marble fireplace surround.
This should reveal the lugs holding it to the wall.
Step 2 locate the studs in the wall with an electronic stud finder.
If smoke staining residue or yellowing can still be seen based on how long the smoke has been allowed to permeate the surface you can use mineral spirits or white spirits for our uk friends in equal parts with distilled water and spray on the surface.
To start removing one of these fireplace surrounds you will have to chip away the plaster around the edge of the mantelpiece.
You can then go about removing the screws which should start to release the surround from the wall.
Step 5 removing the chimney.
Run the blade of a utility knife along the seam where the fireplace surround meets the wall along both sides and the top.
Lightly rub the stain with the cloth increasing in pressure if the stain is stubborn.
Or just attack it with a hammer.
Here are some more general tips for getting those pesky stains off your lovely marble fireplace or surround use a soft microfibre cloth to remove surface dust and dirt.
Make sure to cap off the chimney before covering over the interior area where the marble fireplace surrounds has been removed.
That will be on the wall with adhesive and need levering off wall gently if u don t want to damage it.
Once removed u can see behind the surround.
Removing the old fire surround if the fire surround is screwed to the wall through metal lugs buried in the plaster chip away an inch or so of plaster all around the edge with a cold chisel and club hammer.
Use warm not hot water.
Place sticky notes on the wall where the studs are.