Summarize:

When the app opens, you'll immediately see the other Waze users that are driving near you. " First, click the Menu button. From the Menu, select the gear-like "Settings" wheel. " This should reveal all of the relevant settings. You only need to perform this step if you're using Windows Phone 8 rather than Android or iOS. " This menu will allow you to tweak volume settings. There should be a sliding bar next to "Prompts volume." Slide to the left to decrease volume, and slide to the right to increase volume. You can also click "Play Sound to Phone Speaker" if you'd like to use an external speaker.
Open Waze. Navigate to "Settings. Swipe left to "All. Click on "Sound. Adjust the volume.