You need to go to the SUPPORT site for that laptop and find the correct drivers.
you can either:
1) manually download the driver you need from the Dell support site for that laptop, or
2) run the Dell Solutions Center (or whatever its called) software that manages updates for your Dell laptop. It should automatically update drivers.
*If you added your own copy of Windows 7 64-bit (not Dell) and have an NVidia graphics chip you probably can install the latest NVidia driver: http://www.nvidia.com/object/notebook_drivers.html (If you have an NVidia GPU it will scan for it here to locate the best drivers)
Otherwise you likely need to find the driver at the Dell support site for your exact laptop if your GPU is Intel or AMD.