You will have to modify index.php and the layout.css, of the template.
You could add a new div just after mainwrap, e.g.
<?php mosLoadModules('slider', -2); ?>
Then you will comment the
After that you can add in layout.css just above the id oktoheader a new id for header
and any css that you need.
Finally because I used the name slider as a module position, you will go to SITE > TEMPLATE MANAGER > MODULE POSITIONS on the menu as admin and add a new position named slider
to the list at the end.
After that, go to modules and change the position of the module to slider
and that should do it.