Download Google's Ringdroid app and use it to create the tone you want and you will be set. Super easy. I have my Father use this app and if he can use it anyone can.
Hook the phone up to your computer via USB - search for the music file and move it to the Ringtones/Notifications folder. It should then be available to use and set and your ringtone.
Another alternative is to get the Zedge app, and you can then customize and download all kinds of ringtones, notification sounds, wallpapaers, etc.