When you hit the icon on Orders interface toolbar, a new window opens up with the details of orders grid for you to print.
You can modify this print screen by editing a specific file, but beware that you need to have a little knowledge of CSS. Here is how.
Create the following folder and file in (/xxx/ corresponds to a series of letters/numbers specific to your installation):
Copy/paste the following data in the settings.php file:
$ord_PrintView_Before = '
Modify the CSS code you wish to use.