Possible to change post author?

Wondering if I can change the author of a post?  I know that it changes if you modify the name on a user profile and it changes to Guest if you delete a user, so I'm wondering it it's possible to change for other reasons (i.e. someone posted general information useful to other forum members, but that person is no longer welcome on the forum....OR, responsibilities for an activity have shifted and you want the new person to be able to edit the original post).