How do I replace my mantle?

Excuse me, I'm having a bit of trouble with replacing my mantle. Could you possibly explain the steps to me? I'm not quite sure where to start. Is there a specific way to remove the old one? And once that's done, how do I ensure the new mantle fits properly? Also, are there any tools or materials I need to have on hand? It would be greatly appreciated if you could guide me through this process. I'm not very experienced with this kind of thing, so your help would be invaluable.