OroCommerce give you the ability to customize your header by combining many components and bundles like layout service management and other , first go to file : vendor/oro/customer-portal/src/Oro/Bundle/CommerceMenuBundle/Resources/views/layouts/blank/page/top_nav.yml
you need observe that is inside blank basic theme (the big parent of default and custom and other theme) the content is :

 
layout:
    actions:
        - '@setBlockTheme':
            themes: 'top_nav.html.twig'
        - '@addTree':
            items:
                top_nav_container:
                    blockType: container
                    siblingId: ~
                    prepend: true
                top_nav_menu_container:
                    blockType: container
                top_nav:
                    blockType: menu
                    options:
                        item: '=data["menu"].getMenu("commerce_top_nav")'
                        allow_safe_labels: true
            tree:
                page_header:
                    top_nav_container:
                        top_nav_menu_container:
                            top_nav: ~
​

the file related to this .yml is  top_nav.html.twig , you can see 2 container and one block , the tree used to orgnize the rendering inside twig :

 
{% block _top_nav_container_widget %}
    {% set attr = layout_attr_defaults(attr, {
        '~class': " topbar"
    }) %}
    <div {{ block('block_attributes') }}>
        <div class="container-fluid">
            {{ block_widget(block) }}
        </div>
    </div>
{% endblock %}
{% block _top_nav_widget %}
    {% set attr = layout_attr_defaults(attr, {
        '~class': " topbar-navigation"
    }) %}
  {% set child_attr = layout_attr_defaults(child_attr, {
        '~class': ' topbar-navigation__item'
    }) %}
    {% set link_attr = layout_attr_defaults(link_attr, {
        '~class': 'topbar-navigation__link'
    }) %}
     <div class="topbar-navigation-wrap">
        {{ block('menu_widget') }}
    </div>
{% endblock %}
{% block _top_nav_menu_container_widget %}
    {% set attr = layout_attr_defaults(attr, {
        '~class': " pull-right"
    }) %}
    <div {{ block('block_attributes') }}>
        {{ block_widget(block) }}
    </div>
{% endblock %}
​​

but we get content of block with : 

​​

 
                        item: '=data["menu"].getMenu("commerce_top_nav")'
​​

what's this easy here we use the menu data provider with alias 'menu' and we have called the function
getMenu() , if you go to services,yml you can find the declaration of service :
​

 
    oro_commerce_menu.data_provider.menu:
        class: 'Oro\Bundle\CommerceMenuBundle\Layout\DataProvider\MenuProvider'
        arguments:
          - '@oro_menu.builder_chain'
        tags:
            - { name: layout.data_provider, alias: menu }
​​

the content of class is :

​

 
<?php
namespace Oro\Bundle\CommerceMenuBundle\Layout\DataProvider;
use Knp\Menu\ItemInterface;
use Knp\Menu\Provider\MenuProviderInterface;
class MenuProvider
{
    /** @var MenuProviderInterface */
    private $provider;
    /**
     * @param MenuProviderInterface $provider
     */
    public function __construct(MenuProviderInterface $provider)
    {
        $this->provider = $provider;
    }
    /**
     * Retrieves item in the menu, eventually using the menu provider.
     *
     * @param string $menuName
     * @param array  $options
     *
     * @return ItemInterface
     */
    public function getMenu($menuName, array $options = ['check_access' => false])
    {
        return $this->provider->get($menuName, $options);
    }
}
​​

but what's 'commerce_top_nav' ? Easy :

1 - the menu name you can find inside vendor/oro/customer-portal/src/Oro/Bundle/CommerceMenuBundle/Resources/config/oro/navigation.yml
the tree is :
​

 
            commerce_top_nav:
                type: commerce_top_nav
                scope_type: menu_frontend_visibility
                children:
                    telephone: ~
                    free_shipping: ~
​​

and content is :

​

 
            telephone:
                label: 'oro.commercemenu.frontend.navigation.items.telephone.label'
                extras:
                    position: 10
            free_shipping:
                label: 'oro.commercemenu.frontend.navigation.items.free_shipping.label'
                uri: '/about'
                attributes:
                    class: topbar__controls
                linkAttributes:
                    class: cart__promo__link
                extras:
                    position: 20
​​

2 - For edit manually you can go to admin System -> Frontend Menu -> click on the link  commerce_top_nav 

i think that is great ….