how do i download to my mp3?

i have just bought a black inovix player and voice recorder 64d from a friend, however he didn't have the instruction book etc, how do i download music to it? i have a mac. i have put it in the usb port and managed to delete some tracks already on but i cant load my own it keeps coming up that there is not enough space although there is only 4 tracks on it. help!!!!!! does anyone have an instruction manual that they can photocopy ?