Your Lenovo B is equipped with a microSD memory card slot. If your laptop or personal computer is compatible with that kind of card (Most laptop computers are so-equipped), you should be able to transfer music files
The Lenovo B is a smartphone. Most smartphones let you store any music file you could find online by touching and holding your finger on it and selecting 'save.' Once a music file is added to your memory card, all you have to do is, again, touch-and-hold it and choose 'assign' from the contextual menu.
The Lenovo B is an Android smartphone and the Android market offers a bunch of free ringtone apps such as MP3 Ringtone Maker, Myxer and more.
Learn more about making your own free ringtones
Here is a sample of the all free ringtones (compatible with your Lenovo B) we offer:
Free 'Unclassified' Ringtones Free Ghost Ringtones Free Short Ringtones Free Techno Ringtones Hear All Our Free Polyphonic Ringtones