updating outline numbering

I have a portion of a document that uses outline numbering
like so:
7.1 xxx
7.1.1 xxx
7.1.1.1 xxxx
7.1.1.2 xxxx
7.1.2 xxx
7.2 xxx
7.2.1 xxx
etc.

Numbering is style-based, so "7.1" is a "Heading 2",
"7.1.2" is a "Heading 3", and so forth. I copied this
block of text to a new document, added a "Heading 1" on
top (which has a value of "1.0"), did a "select all",
pressed F9 to update and... nothing happened. I expected
the 7.1 to change to 1.1, etc. If I re-apply Heading 2 to
the line containing 7.1, then it does change to 1.1, but I
do not have any desire to do that to every line in my
document. How does one tell the document to renumber
automatically...?