How can I resize the back ground of the header?

Hello,

I have this problem: the background image that I need to put in the header is being compressed to the predeterminated space for the background header of the template and cant be completely displayed. How can I make the image for the header would be displayed complete? This is my provisional url:
209.62.36.13/~aquituev/nueva-alianza/
Besides, buttons of top menu are blocking the background of the header. How could I make them smaller, I mean shorter or not so high?
I really will appreciate your support.

Hi doing so wold require lot of template changes because that area has lot of dependent objects , so you will have to adjust your image to fit template.

And what about to make the tabs not so high, smaller. Is that posible. I mean, I'm going to make the image fit in the template, but I would like to have tabs shorter as posible. Is it posible?

Well, here is hint but you will need to adjust it:
Properties that are red are changed/added

Add this:
#nav{
margin-top:18px;
}


Modify this:
#nav li:hover, #nav li.active {
top: -3px;
position: relative;
height: 33px;/*It was 53*/
}

#nav > li {
float: left;
position: relative;
margin: 0 10px 0 0;
height: 30px;/*it was 50*/
-moz-border-radius-topleft: 5px;
-webkit-border-top-left-radius: 5px;
-moz-border-radius-topright: 5px;
-webkit-border-top-right-radius: 5px;
border-radius: 5px 5px 0 0;
behavior: url(templates/hot_architecture/css/PIE.php);
border-top-left-radius: 5px 5px;
border-top-right-radius: 5px 5px;
border-bottom-right-radius: 0px 0px;
border-bottom-left-radius: 0px 0px;
}

that is all in template_css.css

Thank you very much! I really appreciate you take the time to attend my questions because I'm a begginer.

Bye