Clearing bit 7?

From: Forrest (gmauslander_at_hotmail.com)
Date: 07/24/04 

Date: 24 Jul 2004 14:37:10 -0700

I've discovered some ancient text files that would be plain ASCII had
not their characters' high bit gotten set by some bizarre accident.

Is undoing this sort of damage something that can be addressed easily
from the command line, or will programming be required? (Google is
intimating the latter, but maybe I phrased the queries badly.)