The U sports a microSD memory card reader. If your laptop or personal computer can also read that card format (Most notebooks are so-equipped), you should be able to transfer music files
The U is a smartphone. Most smartphones should let you save any mp3 song available online by touching and holding your finger on it and selecting 'save.' Once a music file is stored on your library, touch-and-hold it and choose 'assign' in the contextual menu.
The LG U is an Android smartphone and the Android market offers a bunch of free ringtone apps such as MP3 Ringtone Maker, Zedge and more.
Your LG U is Bluetooth-enabled. Bluetooth is a wireless protocol which lets you connect your cell phone to other Bluetooth-enabled devices. If your computer is also Bluetooth-enabled, simply connect both devices and transfer any music file from your computer to your LG U.
Here are links to some of the free ringtones (compatible with your LG U) we offer:
Free Horror Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Hear All Our Free Polyphonic Ringtones