you need to adjust it in windows first. go to control panel>sounds and audio devices>voice>voice playback advanced. follow the directions from there to test and adjust.
then readjust it in the game if necessary.
also try to make sure that when you are speaking your talking directly into the mic not with it set off to the side of your mouth. some of the less expensive mics will have a harder time picking out your voice from the rest of the background noises if you are not speaking directly into it.