You can modify the header and footer in templates\css\style.css

#header {
width:100%;
padding: 0;
margin: 0;
}

#footer {
width:auto;
display:block;
}

For modifying menu background edit templates\css\style.css and findout following


#menu {
width: 100%;
margin-bottom: 2em;
margin-top:2px;
background-image: url("../images/menu.gif");
}


Keep backup before modifying files