Noise reduction can be turned on or off by selecting "Noise reduction > Noise reduction" in the menu.
The noise reduction level can be adjusted with the "Noise reduction > Reduction level" item in the menu. Larger values will reduce the noise more, but values that are too large will distort the signal and make it harder to understand (since some of the signal will be classified as noise and removed). A value of around 50-65 is often a good starting point. Values much above 80 are likely to distort speech too much, but may be useful for CW.