One of the easiest ways is to open the current Dreamweaver web (assuming you still have copies of the original web files, open one of the pages then save it as a different page name. This gives you the original page layout with all hyperlinks to the other pages.
Add a hyperlink to your new page from any others that needf to link to it and upload the site again to the web server it is on.
Make sure you keep a working copy of the site as a backup in the event of something going off the rails.
Once a site gets past a simple half dozen or so pages it becomes worthwhile to look into Dreamweaver templates. Basically, you make a page template that has all the site navigation hyperlinks, overhead banner or logo, footer with copyright statement and so on. Link all the pages in your site to the template then when you want to make any changes, alter the template, apply it to all pages and they all get the same commmon elements contained in your template and the page content is all that differs.