You should be able to update the page number field by switching between Page Layout view and Print Preview view.
But be warned about inserting the page number using the Insert, Page Number dialog. It is quick, but it inserts the page number in a floating text box (complete madness!).
Instead, use View, Headers and Footers, switch to the Footer, and then click on the Insert AutoText button on the Header & Footer Toolbar and select page x of y. This inserts fields correctly. If you don't want the number of pages, just delete the field.
Regards: tf1