this video will show you how to reduce polygons with Delete Loops.
you may want to use this method if zbrush reconstruct subdivision does Not work,
you may want to use this method if you dont want to QRemesh it if your model all ready has good edge loops.
the end results you should have lower polygon counts and your higher detail preserved.
video http://youtu.be/9J1jALIXVpM?hd=1