The Avid 4 features a microSD memory card slot. If your personal computer is compatible with that type of card (Most notebooks are so-equipped), you should be able to save music files
The ZTE Avid 4 is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Zedge and more.
Here are links to some of the free ringtones (ZTE Avid 4-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones