removing music but not voice

how can I remove music and stay only with the voice?

You could try the “Vocal Reduction and Isolation” effect: http://manual.audacityteam.org/man/vocal_reduction_and_isolation.html

If that doesn’t work, then you would probably need to use expensive specialist software such as “Melodyne” (http://www.celemony.com/en/melodyne/what-is-melodyne)