Ok thanks Robin, I’ll try that too!
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