Go to Online Store > Navigation.
Click on the name of the navigation you want to edit.
You can add new items to the navigation by clicking the Add new menu item link.
You can delete/edit items by clicking on the pencil or trash can icons on the right.
You can sort items by dragging them from the icons on the left.
When you've made the changes, click the Save button.
Adding new navigations
You can also add new navigations from Online Store > Navigation > Add navigation if you wish. You can then use the new navigation in the theme. See below for more detailed instructions 👇
How to use the navigation in your theme
In the theme of your online store, there are sections where you can choose which navigations are used in your online store. These options can be found in the header and footer of the online shop. The header may also have a separate selection for which menu is used in the mobile view (depending on the theme).