Within the editing page, click 'Edit Links' on the left.
To edit a link or heading, click 'Edit'. To delete a link or heading, click the red 'X'. To sort your links and headings, use the arrows under 'Sort' to drag the link up or down to where you'd like them in the list.
Make sure to save your changes by clicking the green 'Save' button at the top right or bottom of the page.