On Mac OS X the graphics driver is part of the operating system. You can only upgrade by upgrading to a newer version of the operating system.
 
1. Click on the Apple logo, in the upper left corner and select ‘About this Mac’.
(Refer attached image for details)
 
Note: If you click on ‘More Info...’ you can find out which Graphics/Display you are currently using.
 
2. If you want to update your system, back in the ‘About This Mac’ dialog, click "Software Update."
 
3. If there is a Mac OS X update available, you can install it. If there is a graphics driver update, it will be included in the Mac OS X update.