[all variants] How to install ATI graphics drivers (no additional drivers under software sources)?

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http://ubuntuforums.org – I am using ubuntu gnome remix 12.10 with ATI mobility radeon HD 4300 graphics card. Software sources do not show any additional drivers. How do I install the graphics drivers for my system? $ lspci | grep VGA 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI RV710 [Mobility Radeon HD 4300 Series] (Hardware)