Nokia Lumia 520 - How do I install a ringtone using the Angry Birds Roost application?

Browse to the download section in the main panorama. Browse for a ringtone you wish to use. Tap on the download button next to the ringtone you wish to install. After the download is complete, tap on the install button. Name the ringtone and check the box to set as your current ringtone and then tap the OK button.