How do I reorder items in a navigation menu?
A common way to build a navigation menu is to output links to the assets in a particular Folder. That kind of menu follows the order of items within the Folder.
To change that order, see Folders.
If reordering the Folder has no effect on your menu, the menu is being generated some other way — alphabetically, or from a static XHTML Block, for example. Reach out to your CMS or Site Administrator to find out how that menu is built.
After updating a navigation menu, publish all pages in your Site that contain it, so every page on the live site picks up the change.