The best way is to design your navigation then put it into a server-side include file (with the ending .shtml). There are different ways to do that depending on the software you're using to create your web pages. I use Dreamweaver CS3 and all I have to do is click on "Insert/server-side include", choose the navigation file from the pop-up file list (navigation.shtml) and that's it.

Since the navigation file name never changes, you just change the buttons and/or links in the nav file and re-upload it whenever you change it, and it's automatically changed on every page.