Deidre, what are the stairs like now, under the carpeting? There have been several recent posts about this subject, so you might want to check the search feature also.
In many cases, you can remove the old tread and replace with new oak treads that are available from stock in home centers. You could have treads of other kinds of wood milled to shape. It is generally easier to prefinish the treads before installation, but your stairs will dictate what can be easily done. That's a brief rundown on the subject. Look at your stairs by removing drawers under them, from another floor or set of stairs, or similar detective work and let us know what you are starting with.