Your Grand Mini has a MicroSD memory card slot. If your personal computer has a slot for that card type (Most laptops are so-equipped), you should be able to save a music file
The Grand Mini is a smartphone. Most smartphones will let you save any song found online by tapping and holding your finger on it, then selecting 'save.' Once a music file is saved to your media library, tap-and-hold it and select 'assign' from the drop-down menu.
The BLU Grand Mini is an Android phone and there are plenty of free ringtone apps such as MP3 Cutter, RingDroid (open source) and more.
More on free ringtones
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