octave shift

Select just that voice, then press Ctrl+Up. To select just the voice, that depends on if you literally mean one voice within one staff or if you really mean the whole staff that happens to be dedicated to one voice part. For the latter, select the full staff: click first measure, Ctrl+Shift+End to select to the end of the score. To select only one voice, right-click one note of the voice, Select / More, check the boxes for Same voice and Same Staff. There are other ways, too.