The Tank Xtreme Pro has a MicroSD memory card reader. If your personal computer can also read that card type (Most notebooks are so-equipped), you should be able to save music files
The Tank Xtreme Pro is a smartphone. Most smartphones will let you save any mp3 song available online by touching and holding your finger on it, then selecting 'save.' Once a music file is stored on your library, tap-and-hold it and select 'assign' in the contextual menu.
The BLU Tank Xtreme Pro is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, Zedge and more.
More on free ringtones
Here are links to some of the 100% free ringtones (BLU Tank Xtreme Pro-compatible) offered here at MartinsRingtones.com:
Free 'Unclassified' Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones