Your theme determines the content that displays in your header and footer. You can edit certain aspects of both your header and your footer in your Store Editor app. To do so, go to your Store Editor app and visit the Content section. From this point, the steps to follow depend on your theme. You'll find settings under the Header and Footer menu selections. Specific options available vary by theme.
Keep in mind that you can add, edit, or remove navigation menu links easily. For more information, see "Store Editor App: Menu".