They are located in the bottom half of the Effects menu. The main thing you should do is change up the ratio, but you can also change up the noise floor and threshold if necessary.

Increasing the Noise reduction slider should greatly improve audio quality.Open the Effect menu at the top of the screen.If you want to edit the whole file, press Ctrl+A on Windows or Command+A on Mac. You can do this by clicking on one end of the segment and dragging the mouse until you reach the other. Select the segment of the audio file you’d like to edit.Click on the file you want to edit, then click Open.At the bottom of the window, change Files of type to All supported types. After downloading and starting Audacity, follow these steps: