It may not be possible. It depends entirely on whether ot not your television lets you disable overscan (i.e. set 1:1 pixel mapping) when on HDMI input.
How you do that will vary from brand to brand, and often between models within the brand. If you specify which model you have, I can try to figure it out from the online manual.
You'll know when you succeed, as the desktop will then be surrounded by empty space on the screen. Then you need to tell Catalyst to stop compensating for overscan. In CCC, under the My Digital Flat-Panels section, select the Scaling Options page. There will be a slider labelled Underscan/Overscan, which you need to move to the far right at 0%.
If your television does not support 1:1 pixel mapping over HDMI, then you're stuck with poor quality or VGA.