WordPress cambia los elementos de la lista de navegación del encabezado a div

Quiero cambiar todas las etiquetas ul, li en etiquetas div de wordpress header.wp_nav_menu() siempre devuelve ul, li. Esto es lo que quiero cambiar.

<ul>
  <li>Home</li>
  <li>Services</li>
  <li>Products</li>
</ul>

Esto debe ser un cambio como este.

<div>
  <div>Home</div>
  <div>Services</div>
  <div>Products</div>
</div> 

Por favor, ayúdame. Gracias.

Necesitas un andador personalizado para hacer eso, una versión modificada de Éste respondido por toschosimplemente pegue esta clase en su functions.php

class Description_Walker extends Walker_Nav_Menu
{
    function start_el(&$output, $item, $depth, $args)
    {
        $classes = empty($item->classes) ? array () : (array) $item->classes;
        $class_names = join(' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );
        !empty ( $class_names ) and $class_names=" class="". esc_attr( $class_names ) . '"';
        $output .= "<div id='menu-item-$item->ID' $class_names>";
        $attributes="";
        !empty( $item->attr_title ) and $attributes .= ' title="'  . esc_attr( $item->attr_title ) .'"';
        !empty( $item->target ) and $attributes .= ' target="' . esc_attr( $item->target     ) .'"';
        !empty( $item->xfn ) and $attributes .= ' rel="'    . esc_attr( $item->xfn        ) .'"';
        !empty( $item->url ) and $attributes .= ' href="'   . esc_attr( $item->url        ) .'"';
        $title = apply_filters( 'the_title', $item->title, $item->ID );
        $item_output = $args->before
        . "<a $attributes>"
        . $args->link_before
        . $title
        . '</a></div>'
        . $args->link_after
        . $args->after;
        $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
    }
}

llamar wp_nav_menu en header.php como seguir

wp_nav_menu(
    array (
        'menu' => 'main-menu',
        'container' => 'div', // parent container 
        'container_id' => 'my_nav', //parent container ID
        'depth' => 1,
        'items_wrap' => '%3$s', // removes ul
    'walker' => new Description_Walker // custom walker to replace li with div
    )
);

<ul class="navbar-nav mx-auto">
        <li class="nav-item dropdown active dropdown-slide">
          <a class="nav-link" href="#"  data-toggle="dropdown">Home
            <span>/</span>
          </a>
          <!-- Dropdown list -->
          <div class="dropdown-menu">
            <a class="dropdown-item" href="index.html">Homepage</a>
            <a class="dropdown-item" href="homepage-two.html">Homepage 2</a>
          </div>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="speakers.html">Speakers
            <span>/</span>
          </a>
        </li>
        <li class="nav-item dropdown dropdown-slide">
          <a class="nav-link" href="#" data-toggle="dropdown">Pages<span>/</span></a>
            <!-- Dropdown list -->
            <div class="dropdown-menu">
              <a class="dropdown-item" href="about-us.html">About Us</a>
              <a class="dropdown-item" href="single-speaker.html">Single Speaker</a>
              <a class="dropdown-item" href="gallery.html">Gallery</a>
              <a class="dropdown-item" href="gallery-two.html">Gallery-02</a>
              <a class="dropdown-item" href="testimonial.html">Testimonial</a>
              <a class="dropdown-item" href="pricing.html">Pricing</a>
              <a class="dropdown-item" href="FAQ.html">FAQ</a>
              <a class="dropdown-item" href="404.html">404</a>
            </div>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="schedule.html">Schedule<span>/</span></a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="sponsors.html">Sponsors<span>/</span></a>
        </li>
        <li class="nav-item dropdown dropdown-slide">
          <a class="nav-link" href="#"  data-toggle="dropdown">News
            <span>/</span>
          </a>
          <!-- Dropdown list -->
          <div class="dropdown-menu">
            <a class="dropdown-item" href="news.html">News without sidebar</a>
            <a class="dropdown-item" href="news-right-sidebar.html">News with right sidebar</a>
            <a class="dropdown-item" href="news-left-sidebar.html">News with left sidebar</a>
            <a class="dropdown-item" href="news-single.html">News Single</a>
          </div>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="contact.html">Contact</a>
        </li>
      </ul>