First of all, you must activate the module from your Back Office. From your back office go to Configuration > Your modules > Order taken settings > Order name.
Then just follow the next steps:
1. Click on the transaction number at the top right of the order screen.
2. It will appear a pop-up with the name of the order.
3. Change it and click on Validate.
You can also activate a module so every time you open a new order it asks you to change the name of the order by default. From your back office go to Configuration > Your modules > Order taken settings > Automatic order name.