As V@no has already advised, I believe that GD is only available bundled with PHP.
To see if it is installed with your PHP config, create a file named phpinfo.php containing:
<?php
phpinfo();
?>
upload this to your webpages root directory on your server and then using your browser navigate to this file (eg
www.mywebsite.com/phpinfo.php.
This should then display all the info about php as currently set up on your server. To check for GD look for :
in the screen output. If the GD info is as displayed (or similar with no errors) then GD is installed.
If GD info missing, then this needs to be called in the php.ini file with a reference to the correct php extension file. If you do not have access to, or cannot get anyone to amend the php.ini file, I think you are stuck.