If they are individual, upright conical plants, its difficult to do crown reduction pruning without flat topping them and spoiling the natural form and beauty. You can prune down the tallest leaders a little, conservatively, to suppress the vertical growth somewhat, rounding them off at the top, but the upright growth habit will prevail in the long term.
If the plants are hedged already, consider using the "drop crotch" pruning method. Which means you drop back to a crotch to make your reduction cut instead of shearing off at the same level with hedge shears.
Take hold of the tallest or longest branch, wiggle it and follow it back inside of the foliar mass, to where it joins with a lateral branch. Cut it there, inside the foliar canopy in order to thin at the same time and hide the cut. Continue like that with a target shape in mind, drop crotch the longest and tallest growth down and in, one by one. The result will be a more natural look that with shearing.
Pruning junipers to preserve a natural look is challenging even for professionals and is an acquired skill. Consider hiring an artistic arborist, aesthetic pruning specialist.
Juniper can not tolerate hard pruning. Never cut in to the old wood. It will not leaf back out. You should only trim the green new growth.