I have tried changing the name First Data both in the translation area and in the FirstData payment plugin Title (trying to change it to 'CreditCard' since not everyone knows what FirstData is), but for some reason it still shows "first Data" when you chose your payment method for checking out.
Thanks
Dan
Please look at language /en-GB folder of your site, you will see a file called os_firstdata.ini. Please change the text on that file and It will work as expected (or maybe you can simply delete that file and it will work fine) .
