[@bertbig Participant 12 years, 2 months ago]

I seemed to have solved the problem myself: #happy.
I have made a child theme of twentyfourteen.

And edited the style.css in the child theme; I added this code:

.site {
margin: 0 auto;
}
.site-content .entry-header,
.site-content .entry-content,
.site-content .entry-summary,
.site-content .entry-meta, .page-content {
 /* Original max-width: 474px */
 max-width: 80%;
}

The code makes the content area wider and centers the whole website, which was a wish on my list!

Cheers!

Bert