Any MP3, AAC or Ogg Vorbis file can be made into a ringtone simply by copying it into a folder in storage called "ringtones". It can be /ringtones or /media/ringtones or /foo/bar/ringtones - well, you get the picture.
If you want it to be a notification tone, make the folder name /notifications and, if you want it to be an alarm, make it /alarms
Any files in those folders will be included in the tone picker when you look to choose a ringtone/notification tone/alarm tone.
You can use a third party app like ES File Explorer to do this right on the phone, or do it from your computer if you are tethered.