How can I raise up the render quality in Live Rendering?

I've tried to modify total time, iterations per Frame with many different values, but the result in terms of quality of the image is quite the same. The same thing with the output format: Jpeg, PNG...
The size of the images is more or less the same (1Mb). Maybe I didn't see the correct options.
Is there any option to set the quality of the output image? What kind of render quality can I achive with this app?