To adjust depth, you can change the frequency of your probe and set the depth of the image displayed.
Three frequencies are available (3.5MHz, 5MHz, 7.5MHz) at the bottom of the screen: depth is inversely proportional to probe frequency.
To adjust the gain, select the Gain parameter at the bottom of the screen, which brings up a sidebar on the screen. You can adjust gain by sliding the slider on this bar vertically.