Hedges Out Of Control - When and How to Prune
The first thing that jumps out at me is a problem that a lot of people do. Done properly, the tops should be slightly narrower than the bottom so that the lower branches will get adequate light.
You will need to do the pruning in several gradual steps in either of two ways. Take just a couple of inches- almost but not quite into the brown interior. EASY, too much and you will have big brown spots. I know, it seems like you are not accomplishing much. Or, an alternative would be to reach into the shrub and selectively prune the branches individually to thin the top which will also let in more light into the interior of the shrub. Look in a pruning book for examples of how to cut at a side branch. Also lightly fertilize and water to encourage new growth.
You should see new growth in a few weeks. After the shrub "recovers," you can do it again in late summer but not into fall. You don't want freezing weather to hit any new growth put out after the second pruning.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!