Since you have an Android device, you have quite a few options available. The Google Play Store has plenty of ringtones to choose from. Should you want something a little more customized, you can also record your own.
If you have music files you'd like to use, there are apps available that allow you to cut the files to particular segments or sizes so you can use them as ringtones. For a very brief description of ringtones and possible data charges, click on the links below.