to be a litlte more helpful to someone who does not know.
There is usually a service code on your PC or Laptop.
go to the dell webiste (www.dell.co.uk or www.dell.com)
click on support
click on driver downloads
enter your service tag (if you do not have this - enter the product type and model No.)
select the relevant display driver (sometimes there are a few - if you are not sure - down load several - attempt to install, if it fails, try another)
you should be done