Open a karaoke MIDI file in a MIDI sequencer. A sequencer is a computer program that allows you to create, edit and arrange MIDI music tracks.
Go to the track view of your sequencer to see a list of tracks. In a well-constructed karaoke MIDI file, the first track should not contain any music data, but only non-musical data such as the title and author of the song.
Locate Track 2, which should be the the words or lyrics only. In karaoke files, the lyrics -- stored in a separate track -- are synchonized with the melody.
Select Track 2 and copy it.
Locate Track 3, which should be the melody. A solo organ, vibraphone or other distinctive instrument usually is assigned to this track.
Paste the contents of Track 2 (the lyrics) into Track 3, making sure that you merge the data and do not overwrite the melody.
Delete Track 2, which is no longer needed.
Save the file with the extension ".mid" to identify it as a standard MIDI file. The other tracks are okay as is. They contain the other instrument parts such as piano, drums, guitar, and strings.