Thanks. Currently the overall width of the theme you are using is set for a maximum of 980px and that is about the maximum width for a 1024px wide display resolution, and there are still a good number of people using that resolution.
The theme you are using is a responsive design which means that it adjusts to the width of the screen you are viewing it on (with the max set at 980px). If you widen and narrow your browser window you will see how the responsive theme reacts to different display widths.
For the easiest reading, it is best to keep content widths no wider than about 600px.
You can set things a bit wider if you wish, but keep in mind the width of the textual content. This will widen the maximum content width by 100px.
.site-main, .site-footer {
max-width: 1080px;
}
.content-area {
max-width: 830px;
}
.entry-header, .search .page .entry-header, .entry-content, .entry-summary, .single div.entry-meta {
max-width: 720px;
width: 100%;
}