How to change the labels of login form?

-- url of the page with the problem -- : mywebsite.com/mypage
-- HikaShop version -- : x.x.x
-- Joomla version -- : x.x
-- PHP version -- : x.x.x
-- Browser(s) name and version -- : XXXXX x.x.x
-- Error-message(debug-mod must be tuned on) -- : Error_message

Hi,
I need the user logins with the email instead of his user name.
How can I change it?

I have attached the screenshot where I need these changes.
thanks in advance
Leonora.

I don't know why now its running ok. I supose that the file of translation weren't recognized for some reason (?)
But it's solved!
Thanks
Leonora.