How hard is it to replace a mantle?

Could you elaborate on the complexity of replacing a mantle? Is it a straightforward process, or does it require specialized skills and equipment? What factors might contribute to the difficulty level, such as the material the Mantle is made of or its location within a larger system? Is it something that can be done by a DIY enthusiast, or does it necessitate the services of a professional? And finally, how long can one expect the process to take from start to finish?