How to edit my theme for full width?

yes, go to your /wp-content/themes/manifest_v1.1/style.css and edit the following IDs to look like this:

#siteWrapper{
  margin: 0 auto;
  padding-top: 15px;
  width: 97%;
  text-align: center;
  position: relative;

}

#coreContent{
  float: auto;
  width: auto;
  margin-top: 8px;
}

#footer{
  width: 97%;
  margin: 40px auto 0;
  padding: 20px 0 35px 0;
  border-top: 4px double #ccc;
  color: #666;
  text-align: center;
}

besides that – I see you have some blue image just below this Intef image… I believe one of them is not meant to be there? try this CSS I provided with firebug first to see what you’ll get… or just play with firebug and see how you can change themes appearance and then apply it to style.css