What do you mean by "reference number"?
Why do you want footnote numbers to change? Footnotes are numbered
sequentially throughout a document (or by page, or by section).
If you're referring a second time to a footnote using cross
references, they don't update automatically -- you need to select them
(Ctrl-A) and press F9, or switch to Print Preview and back.
If you have a reference list at the end of your article in the form of
numbered paragraphs that you refer to with cross references in the
text, they also need to be updated manually as above.
