HI Nicolas,
You will have to customize the layout and style to achieve that. This is the idea:
1 - Clone the default layout by duplicating this file:
/templates/ja_mono/tpls/default.php
to have a new file called default-copy.php , for example
2 - Edit this 'default-copy.php' file: to remove the left block and off-set classes
3 - In Backend >> Extensions >> Templates >> duplicate a template style to have a new style >> Layout tab >> select the 'default-copy' layout that you edited above and assign to that article page.
4 - Customize style for this page.
Regards