Audio will default to High Quality on Wi-Fi (Low Quality when using your data). To change that to either 'Always use High Quality' or 'Always use Low Quality':
iOS: On the main navigation at the bottom, tap on 'More.' Scroll down until you see 'Streaming Quality' at the bottom (last option under 'Settings'). From 'Streaming Quality' you can change your audio quality. Android: In the main navigation, scroll down to 'Settings.' From there you can change it.