I have attached external display to my laptop (Dell Vostro 3350 with ATI Radeon HD6470 video card) but image has bad quality: everything is blurred. Where and how to configure that?
Your ATI card is listed as supported by the close source ATI driver (Catalyst)
To install it run
For additional details see
It might be that your second monitor is not running at the native for your display resolution (the one which is recommended).
Try to play with different second screen resolutions:
Press Win (it opens unity dash or gnome-shell overview -- whatever you use) and type in the search box Displays -- it will show Display Settings. Alternatively, click on user menu in the right top corner and choose System Settings, then in the opened window you should see Displays. There you will see both displays and can change the resolution on the second one.
Hope it helps.