When I remove files from my flash drive, the memory isn't cleared, and I can't put new files on- help?

I'm sharing music with a friend, and after filling the flash drive and transferring the music, the available space remains the same even after deleting the files. We started with a 4 gig flash drive, and now it says that there's only a few megabytes left, even though it looks empty! Can you tell me what... show more I'm sharing music with a friend, and after filling the flash drive and transferring the music, the available space remains the same even after deleting the files. We started with a 4 gig flash drive, and now it says that there's only a few megabytes left, even though it looks empty! Can you tell me what the problem is?
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