Select the main folder that contains all the sub-folders that need a different order.
There are five grey tabs that appear: "Name", "Order", "Last Modified", "Last Modified By" and "Actions". Select "Order".
The folders and pages will be numbered. Number one is what is placed at the very top of the navigation. In most cases, this should be the index page, since it is the home page for the entire folder.
To change the order of the other folders or pages, hover the mouse over the item that needs to move. The mouse will change into an arrow.
Drag the item up or down to change the order.