You can change the size of the rectangle and center it like this:
//suppose originalwidth, and originalheight as the starting size, and that you want to set it 40% smaller.
bounds.setSize(originalwidth*0.6F, originalheight*0.6F);
bounds.setPosition( bounds.x+(originalwidth-bounds.width)/2F, bounds.y+(originalheight-bounds.height)/2);
And if you dont want to change the height (it would look like the feet go through the floor), then just do not affect the height:
bounds.width = originalwidth*0.6F
bounds.x += (originalwidth-bounds.width)/2F;