AMD gives this method: (for a windows 7 machine)
How-To Uninstall AMD Catalyst™ Drivers From A Windows® Based System
Last Updates: 6/13/2014
Article Number: GPU-57
This article provides instructions on how to uninstall AMD Catalyst™ Drivers from a Microsoft Windows® based PC system with AMD Radeon™ desktop graphics.
NOTE: The instructions below do not apply to AMD Catalyst™ drivers on AMD APU systems. Systems with AMD APUs do not need to go through the driver uninstall process prior to updating the graphics driver. To update the graphics driver on AMD APU systems, simply download and install the latest compatible AMD Catalyst™ driver. For instructions on installing AMD Catalyst drivers for a Windows® based system please refer to KB article: GPU-507
How to uninstall AMD Catalyst™ Drivers in a Windows® 7 based system
Click on Start
Open the Control Panel
Select Programs and Features
Select ATI Catalyst Install Manager
Click on Change
Click on Next when prompted for the Welcome to the InstallShield Wizard for ATI Catalyst™ Install Manager
Select Express Uninstall All ATI Software
Follow the on-screen directions and restart the system when finished
NOTE! The Windows User Account Control (UAC) will prompt for Do you want to allow the following program from an unknown publisher to make changes to this computer?. Click on Yes to continue with the uninstall process
To verify that the legacy graphics driver has been uninstalled, return to the Uninstall or Change a Program list and ensure that there is no ATI specific software listed
If ATI specific software is still listed, remove any remaining ATI software components using the above process and restart the system when complete
From here:
http://support.amd.com/en-us/kb-articles/Pages/GPU57RemoveOldGraphicsDrivers.aspx#Win7