Change "order sent" email title for "in transit"

[superv]

hi I don't know if it's the right section, I don't know how to use the forum well so I apologize, I wanted a simple help, when I enter the tracking code an automatic email is sent to the customer with the title "Order shipped" being part of the file "in transit" can not be changed in the back office, I wanted to write instead of Order shipped, "order processed and then change the title how can I do? I prestashop 1.6.1.23 , I also inform you that I use the Italian language, thank you