Turn on your computer and open your editing program, such as Reason, Pro Tools, Ableton, Logic or Cubase.
Create or finish the instrumental you wish to move to a single recording track, unless you are importing an instrumental from another composer.
Export or bounce your enitre song as an audio file.
Import the file to its own track in a new project.
Press the record-enable button on the track and begin recording to add sounds to the end of the track to make it longer.
Create separate tracks for vocals or new instruments you wish to add during the recorded instrumental. You cannot record and edit new audio on the same track as the instrumental or you will delete what is already there.