RadeonDriver. This guide shows you how to use the open source Radeon driver for some ATI/AMD graphics cards and APUs, which is part of the xserver-xorg-video-ati package.
This driver provides 2D and 3D acceleration in your video hardware. For the most recent releases of Ubuntu (and its flavours) this driver is usually as fast as the closed-source, proprietary fglrx driver (called AMD Catalyst) from AMD Inc. Furthermore the Radeon driver supports some older chipsets that fglrx does not. The Radeon driver is already pre-installed in Ubuntu.
First, check your graphic card name and chipset: 04 - How can I remove nvidia drivers. BinaryDriverHowto/ATI. How to Install an ATI Driver in Ubuntu.