My understanding of the general practice is that if it is a "major" revision, change the first number, but if it is a "minor" revision, change the second. That being said, in the case you describe, if he is making corrections, changing phrasing, or updating with more current figures, but not changing the general statement of the document, then I would think it a minor revision. If, however, there are important changes in positions or items in the document, then a major revision number change seems reasonable.

Hope that helps.