My mp3 player

Hello,
i have my walkman mp3 player, my laptop detects it, but i tried to delete all the music off of it and put new stuff on the problem i had was the program on my computer said what it was i was wanting to do and when i deleted something it would show up and then when i added something new it would show up like it was meant to but then when i took the mp3 player off the usb nothing had changed, help!!