Good evening. Put your system for the first time, what driver to put for the video card ATI Radeon Sapphire HD 6850? Thank you!
Your card is already supported by the open source drivers included in Elementary OS.
To install updated drivers for all hardware run the following command in a terminal and reboot your system once it completes, reference:
sudo apt-get install --install-recommends linux-generic-hwe-16.04 xserver-xorg-hwe-16.04
To get the latest stable graphics drivers (for better performance and compatibility with newer games) you can add this PPA to your system.