I think you're referring to vertically displayed subtitles.
And to moving them more to the left/right. To be frank: I don't know.
However, I would suppose it works similar as moving horizontal subtitles.
Could you try if [Shift]+[Up] respectively [Shift]+[Down] do the trick?
P.S.:
If you're referring to horizontally displayed subtitles: as far as I know you can't!