If you are tired of the default ringtones on your Galaxy S5, you can easily use the audio files stored on your phone as ringtone (Mp3 files). To set custom ringtone on Galaxy S5 do as follows:
1. Open Music application (the default Galaxy S5's music player)
2. Look for the song you want to set as ringtone
3. Play the song
4. On the playing now window, tap the 3dot icon and select set as.
5. Choose whether to save the ringtone from the beginning or use the Auto recommendation mode
6. Tap Phone ringtone to set the selected music file as the ringtone
7. Tap Caller ringtone and choose a contact afterwards to set the selected music file as the ringtone for a specific contact