If you want to basically just move everything over so it is just like the drive you have now, just drag everything from drive a to drive be, eject drive a and the rename drive b to the exact same name that drive a was.
This works great and I've done it many times. iTunes will still point to the "music drive" it doesn't care what kind of drive it is just that when it goes out and looks for "music folder" on "music drive" it is there.