If you checked "add to template" when you made the change, all new documents
will carry the change, because you changed Normal.dot, which is the template
all new documents are based on.
For already created documents, you will need to redefine the style in each
document. There are several different ways to redefine a style in old
documents:
1) open up each document and do the same thing you just did
OR
2) use the Organizer to copy the changed style definition from the
Normal.dot to the old documents. You would still need to open all the
documents first, but it might be easier--I think you could just leave the
Organizer open and use the drop-down menu in that dialog to switch among the
documents (though I haven't tried that).
For fuller instructions, see:
http://www.officearticles.com/word/using_the_organizer_in_microsoft_word.htm
OR
3) use Insert | File to put the old document into a new blank file based on
the current Normal.dot, which will carry the updated style definitions. I
generally like this method, as it creates a new file and leaves a backup,
which is always handy.
OR
4) re-attaching the template with the new style definition. The same link
as above shows you the Tools | Templates and Add-ins dialog. In that
dialog, you would need to check the "automatically update document styles"
checkbox, and then your doc should pull the new style definition from
Normal.dot. But then you have to uncheck the box, because it generally has
evil effects. I don't recommend this method, and I'm not quite sure whether
you would have to close and re-open the doc or close and re-open the dialog
for it to take effect.
Hope that helps,
Daiya