Driver Cleaner is a software application which will help you remove parts of drivers that are left after uninstalling the old drivers.

The program is for ATI and nVidia drivers. First you need to uninstall the drivers from the control panel than reboot and after that run the program.

If you really want a good description of what steps you should do than you really need to read the readme file included in the zip file and installation as it contains a detailed description step by step.