Look in your template code for your <style> </style> tags. Whatever you need to alter will be somewhere in there. Looking at your source code from my computer, it looks like you can change the width. Look for the following block:
/* -- layout -- */
@media all {
#content {
width: 700px; <----- this might be where you can change the width.
margin: 0 auto;
text-align: left;
background: #fff url(
http://www.blogblog.com/snapshot/bg-body.gif) 0 0 repeat-y;}
}
.................
#main {
line-height: 1.4;
float: left;
padding: 10px 12px;
border-top: solid 1px #fff;
width: 428px; <------looks like you can alter this too, in conjunction with the one above.
/* Tantek hack -
http://www.tantek.com/CSS/Examples/boxmodelhack.html */
voice-family: "\"}\"";
voice-family: inherit;
width: 404px;
Play around with those options. The one immediately above looks like what you'd want to change to make the section where your posts go wider. The one above that (in my examples) would change the width of that and the sidebar.
On my computer screen it looks fine, but there is a lot of negative space (I have a widescreen on my laptop). Because the width appears fixed in the style sheet, it won't change depending on the viewer's screen.