I what to change the background noise to music, at the moment all i can hear is other people speaking and the sound of traffic
I often feel that if you remove the original sound completely, it will be something missing. Reduce the noise so that one feel to be present in the film, can often be better. Then add music.
You can remove the sound completely, by muting the audio track, or select and ungroup picture and sound, then the soundtrack can be deleted.
You can reduce the volume, by moving down the rectangle in the center of the soundtrack.
Then you can add music from a CD or other source.
I agree with asoeli. A video that has background sounds creates ambience which without any of the original audio seems like a moving slide show especially if you can actually see the traffic and people talking. Reduce the camera based audio level, and make the background music louder and you should come up with a decent blend. Now if there is something like wind noise, camera hum or tape hiss, I would definitely remove that first using either the Magix Video Sound Cleaner, or something like "Audacity" to get rid of the really annoying sounds.