I have an AT&T Samsung Galaxy S4 and I've been trying to delete all of the downloaded songs on my phone. When ever I restart my phone all the songs would appear again. So I went to "My Files" and found the folders containing the songs I wanted to delete. (My files>all files>sd memory card) When I tried to delete them, it says "Deleting failed" and the files were all still there. What am I doing wrong and how can I delete all the unwanted files from my SD card?