Unixmen shows you how to install ATI Display driver in Ubuntu

If you're an owner of an ATI GPU, Ubuntu comes with a default driver for most (particularly the newer range of products). However, this out of the box driver lacks many features that the standard flgrx driver package is capable of providing. This driver is not included by default and to enable the advanced computing functions that your GPU supports, it has to be installed.

  Howto install ATI Display driver in Ubuntu