How you translated the files, on the server from your admin or on your local computer?. If you translated on your local computer and want to install them on the server just upload them in ascii mode to your language directory.
Now I understand what you did and what you want, always your posts almost unclear.
Go to your admin - > Language manager, create language name it "French" or as you want to be named, it will be copied from what you have translated. Now set your new language as the default, later you can delete the "English" language but do not do it now.