Switch Navigation Categories

Is there a possibility to make the Navigation of the pages appear in the bar where the Categories are showing?
It would be a plus for my project...

Hi!
Yes it is. To do that you need to change wp_list_categories('title_li=&') to wp_list_pages('title_li=&') in function block_main_menu in the functions.php.

GREAT!

Now is there a way to make the upper navigation disappear?

Also the logo above the navigation is an image, but it's not centralized.
Any way to ajust this?

To make make top menu desappear just remove block

<div id='secondarymenu'><div class='left'></div><?php
$nav_menu_params=array(
'depth'=>0,
'theme_location'=>'sec-menu',
'menu_class'=>'menus menu-top',
'fallback_cb'=>'block_sec_menu'
);
wp_nav_menu($nav_menu_params);
?><div class='right'></div></div>

from header.php file.

And the logo must be centralized. Try to change logo width by editing #logo in style.css. If you changed logo image to your logo just specify width of the your logo image there.

Works like a charm !!!

Thank you for your GREAT help !!!