ZBrushCentral

How fit UV

Hi thanks.
my question is in the area of creating UV
(and fill the largest percentage of the canvas)
the zbrush, leaves the UV scarce and small and does not fill all the space.
How can I do to fill those empty spaces of the UV
And, that when I generate the UV of polygrups, fill the whole canvas as much as possible?
here is a picture below show how i need with green arrows to fill.

Thank you !
.

thanks so much very much
now is working
bless