The get_currentuserinfo function that you're using, places all the information in a global variable called $current_user.
This is how you can retrieve the first name:
$current_user->user_firstname
If you read further down in the function's documentation, there is an example that you can use if you want to use different global values. The example is the following:
<?php global $display_name , $user_email;
get_currentuserinfo();
echo $display_name . "'s email address is: " . $user_email;
?>
So, since you want the first name, I assume that you can get it if you replace "$user_identity" with "$user_firstname" in your code. I have not tested it, but it makes sense from what I've read in the documentation.