How to toggle dropdown arrows

• Use :before pseudo for decorative arrow icons
• Use jQuery's .toggleClass()

jQuery(function($) { // DOM ready and $ alias in scope

  /**
   * Option dropdowns. Slide toggle
   */
  $(".option-heading").on('click', function() {
    $(this).toggleClass('is-active').next(".option-content").stop().slideToggle(500);
  });

});

.option-heading:before           { content: "\25bc"; }
.option-heading.is-active:before { content: "\25b2"; }

/* Helpers */
.is-hidden { display: none; }

<div class="option-heading">HEADING</div>
<div class="option-content is-hidden">
  content<br>content<br>content<br>content<br>content<br>content<br>content
</div>

<script src="//code.jquery.com/jquery-3.3.1.js"></script>

P.S: If you're using some different font-icons (like i.e: icomoon) than add the respective hex codes and also font-family: 'icomoon'; to the :before pseudo.

Use classes!

jQuery(document).ready(function() {
    jQuery(".option-content").hide().removeClass("shown").addClass("hidden");
    jQuery(".option-heading").click(function()
        {
            jQuery(this).next(".option-content").slideToggle(500)
                  .removeClass("hidden").addClass("shown");
        });
});

Then use CSS:

.option-content.hidden{ background-image:url(hidden.png); } 
.option-content.shown{ background-image:url(shown.png); }