Open the includes/templates/YOUR_TEMPLATE/css/stylesheet.css and change the width settings from 750px to your desired width.
Find:
.centershop {
padding: 0px;
margin: 0px auto;
position: relative;
text-align: left;
width: 750px !important;
Change to :
.centershop {
padding: 0px;
margin: 0px auto;
position: relative;
text-align: left;
width: 100% !important;
Find:
TABLE.header {
background-image: url(../images/header_bg.jpg);
background-repeat: repeat-x;
width: 750px !important;
background-color: #ffffff;
border-right: 1px solid #9a9a9a;
border-left: 1px solid #9a9a9a;
border-bottom: 1px solid #9a9a9a;
Change to:
TABLE.header {
background-image: url(../images/header_bg.jpg);
background-repeat: repeat-x;
width: 100% !important;
background-color: #ffffff;
border-right: 1px solid #9a9a9a;
border-left: 1px solid #9a9a9a;
border-bottom: 1px solid #9a9a9a;
Find:
.main_page{
width: 750px !important;
background-color: #ffffff;
border-right: 1px solid #9a9a9a;
border-left: 1px solid #9a9a9a;
border-bottom: 1px solid #9a9a9a;
padding: 5px;
Change to:
.main_page{
width: 100% !important;
background-color: #ffffff;
border-right: 1px solid #9a9a9a;
border-left: 1px solid #9a9a9a;
border-bottom: 1px solid #9a9a9a;
padding: 5px;
and
TD.headerNavigation {
width: 750px !important;
position: relative;
vertical-align:middle;
font-family: Verdana, Arial, sans-serif;
font-size: 11px;
font-weight:bold;
color:#000000;
letter-spacing:1px;
padding: 5px;
To:
TD.headerNavigation {
vertical-align:middle; font-family: Verdana, Arial, sans-serif;
font-size: 11px;
font-weight:bold;
color:#000000;
letter-spacing:1px;
padding: 5px;
Note: there are several places that have width attributes and you need to change all of them.