The question is not “how do I move the slider to the middle of the page?”, but rather “how do I insert some text above the slider?”
In this case, the answer is simple: use a Graphene action hook widget area:
http://blog.kjodle.net/2011/11/04/graphene-action-hook-widgets-an-easy-way-to-modify-your-blog/
As I indicate in that tutorial, you may need to play around a bit to find the right action hook widget area. I would suggest to start with “graphene_before_slider” in “includes/theme-slider.php”.
Hint: wrap whatever you add to that area in a uniquely identified css id. That way, you’ll be able to style it however you like. In your text widget:
<div id="my_slider">
stuff
</div>
In your custom CSS or child theme style sheet:
#my_slider {
style elements go here;
}