Permissions

[dad]

Okay I need some help here. My desktop system is Mint 17.3. The owner 
name of said system is dad.
I bought an 8 gig micro card and named the owner dad. I put music on 
this card in m4a format.
THEN, I bought an mp3 player that ONLY plays mp3's. This player won't 
recognize my m4a files.
I installed a program called sound converter to convert the offensive 
files. The micro card will NOT let me add or delete files to it. 
Therefore I can't convert the offensive files.
How do I get the Micro card I own to accept converted music that I own 
to it?
Checking the ownership of each, says dad own both. What am I missing here?

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