Trouble Deleting Notes

I am going through and editing a song that someone else has created, and one of the staves consists of notes in two different voices (as in they are blue or green when selected, not as in one is a violin and the other a piano). However, I was wanting to lower all the notes in the second voice (green), while leaving the others (blue) as they were. To do this, I added another staff to copy over the notes I want to lower. But, my problem is that I can't seem to find a way to delete the notes in one of the voices while leaving the others as they were. As the song is kinda long, I don't want to have to delete each note separately, and would even struggle with this because some of the blue and green notes are the same note (there is one note with two stems coming of, a green and blue one above and below), meaning to delete the green one I will have to delete the blue one first.

Any help would really be appreciated.