To add that, please edit the /components/com_jfbconnect/libraries/profile/vk.com . Around line 21, you'll see:
'first_name' => 'First Name',
Above that, add another line so it looks like:
'full_name' => 'Full Name',
'first_name' => 'First Name',
That should do it for you. I hope that helps, but if you need anything else, just let me know!
Thanks,
Alex