I do generally take a tabula rasa ("scorched earth") approach to this sort
of problem. If you try to "fix" things, you'll probably end up spending a
lot more time (with less reliable results) than if you remove all formatting
and start from scratch. What I usually do is either print the document out
for reference or at least save the original. Then, on a copy, I remove all
formatting by applying the style that will be used the most in the document
(usually Body Text or Body Text First Indent) and then go back and apply the
headings and such.