Change page width

.post-content {
    float: left;
    width: 88.333em; /*play with this value*/
    overflow: visible;
}

Add the above code to the `style.css’ of your CHILDtheme:

You don’t have a childtheme yet?

1. Install and activate ‘one click childtheme plugin
2. create the childtheme
3. Dashboard > appearance > Themes > activate the childtheme
4. Make the changes in the CHILDtheme!
– copy php files / css-file(s) of the original theme [as required] to the childtheme directory and edit them as required.

YOU ROCK SO HARD

You’re weelcome.
How to find which CSS to change

About finding out ‘which things to change in your site [css / html / php]

Well it’s all a bit like trying to solve a puzzle.
Fortunately there are good tools for that.
In your browser: Install / activate webdevelopment add-ons / plugins.

Recommended: ‘Firebug’ and ‘webdeveloper: https://www.chrispederick.com ‘
These tools will show you what’s what.
e.g. right-click > inspect elements > click left bottom arrow-icon
click item in webpage
Inspect css on the right
alter css values to test effect / result
OK? copy altered css rule
paste it in the style.css of your childtheme.

Alternatively:
Press <F12> a screen will show in the bottom.
Move the mouse over each line
The area shows in the top-half
Press + to unfold parts
Investigate and alter on the right etc.
paste it in the style.css of your childtheme.