For some documents, you may want to have different headings on different pages or different kinds of page numbers (roman, then arabic). The way to do this in a single Word document is to create a new section where you want the changes to take place.
That is done by clicking "insert" and then "break." A window will pop up with page and section breaks. You want the section breaks kind. You can choose from several options but the one you'll want is "next page," which starts your new section on a new page.
You can then treat the new page (and anything that comes after it) as a different document and changing its formatting won't affect the earlier pages.