You cannot seperate recorded tracks from each other once they are combined for a final song. Studios record in tracks, each intrument or sections of intruments and different channels will be recorded as individual tracks. Then vocals can be laid down on seperate tracks as well. Then added into the prerecorded intruments tracks. Then all those tracks get flattened into a final track for album or CD or whatever. Once it is flattened out onto one track, it's nearly impossible to seperate tracks again unless they are just in different isolated audio playback channels or the range and pitch is so different the other parts like intruments.
The only real way to get clean original vocal audio out of a a final song, is to get the original tracks from the recording studio. You'll have to usually have some sort of recording deal with the recording studio to get seperate tracks unless they released it publicly like some songs will release an intrumental version or audio acapella track on a B side or something. You see it alot in singles. The B side may have an intrumental.
There is no system or program currently that I know of that can cleanly and accurately remove vocal from finished musical song. Again, some circumstances like if the recording has tracks isolated in channels. Thats just a matter of balance and isolating a channel. You can hear it in surround sound very well if you go from each different speaker. Unless the recording studio released the original tracks, then I'm afradi theres not a whole lot you can do. Some great engineers can get close to seperating vocals from a recording but most of the times its too much work and mediocre results.