lartomar2002, I am not sure that you can do both things; shape it into a ball and thicken the inner foliage at the same time. Shaping it into a ball is comparatively easy. The youngest leaves are a lighter green and if you prune these only, (weekly?) soon you will have the ball shape. In the meantime the inner foliage will turn brown and eventually drop. To obtain inner foliage it will be necessary to allow light to penetrate the canopy and this can be achieved by removing varying amounts of twigs and branches. You will still be able to maintain a rounded profile but the perimeter will not be as tight as say, a topiary or similarily sculptured specimen.

thank you