how do i make my library transfer using homesharing to one computer? it is only letting me share my library to one computer, but not back to the other?

i just got a new PC and i have used homesharing in the past, but now i cannot. i want to transfer my music from my old PC to my new PC, but when i turned on homesharing, the library (containing only one song) transferred to the old PC, when i wanted the old PC's music to be transferred to the new one. nothing is showing up allowing me to transfer the music from the old computer to the new one. help?