Your DuraXV LTE features a microSD memory card slot. If your personal computer has a slot for that type of card (Most laptop computers are so-equipped), you should be able to save music files
The DuraXV LTE is equipped with Bluetooth version 4.1 (with LE/EDR), which lets you connect to your computer wirelessly. Just pair phone and computer together and drag and drop your audio files from your computer to your Kyocera DuraXV LTE.
If these tricks do not work for you or if you prefer not to buy new accessories, you can always use one of the numerous free '3G Uploader' services available online. A search on Katapulco should retrieve plenty of them. 3G uploaders work as follows: Upload your own free ringtones on their web site and they will provide a temporary web address. Navigating to that URL with your Kyocera DuraXV LTE's browser will download the free ringtone.
Here is a sample of the free ringtones (Kyocera DuraXV LTE-compatible) offered here at MartinsRingtones.com:
Free Horror MIDI Ringtones Free Ghost Ringtones Free Short Ringtones Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones