How can I move all my iTune downloads and downloaded CD to an External Drive and still register in iTunes on my iMac?

I have nearly used up my iMacs 1T drive downloading my CD collection to it, I have a Seagate 1T that has plenty of room on it to transfer my library of music. However I do not know how to A. send the entire music library to a seprate drive, and B. how to run iTune so it still reads the file on another external drive... anyone know to accomplish this effectively?