Slide down and slide up with one link

Slide down and slide up with one link

Hi,
I'm really new to Javascript and jquery and I'm actually writing my first script.
It's for a navigation on my website. I want to have the sub-categories sliding down, if you click on a parent-category. I made it and there's no problem. But I want the sub-categories to slide away with a second click on the parent-category and I don't know how to do this.

to give you an example of my code:
the html:
<ul>
   <li><a href="#">Home</a></li>
   <li class="menuparent"><a class="menuparent2" href="#">Info</a>
      <ul class="sub-categories">
         <li><a href="#">News</a></li>
         <li><a href="#">Calendar</a></li>
      </ul>
   </li>
   <li><a href="#">Contact</a></li>
</ul>

and the js-file:
$(function() {
         $('li.menuparent a.menuparent2').click(function() {
                           $('a.menuparent2 + ul.sub-categories').slideDown('fast');
                           });         
         
         });


I hope you can understand me (my english isn't so good) and I would be very glad if you could help me ;-)