This topic is part of Frontend Menus where you can learn more about all available types of frontend menus, how to configure them on other levels, and edit their items.
To customize one of the default storefront menus (e.g., commerce_main_menu) or customer/partner portal menus (e.g., customer_usermenu):
Navigate to System > Frontend Menus in the main menu.
Click on the menu you would like to edit.
Update the menu contents following the guidelines provided in the Edit a Frontend Menu section.
The changes apply automatically.