How to replace part of the path?

How to replace part of the path?

I'm making a batch processing application that should convert files from
directory A and place them into directory B preserving the same path after
the relative root directory.
Example:
before: C:\MyProject\Files\Input_\file1.cs
after: C:\MyProject\Files\Output\file1.cs
before: C:\MyProject\Files\Input_\folder\subfolder\file2.cs
after: C:\MyProject\Files\Output\folder\subfolder\file2.cs
I hope it's clear what I'm after. Is there a standard method in System.IO
namespace that can do this? If not, how do I implement it?