I would only take a few branches out each year and do the pruning over 3 or 4 years. If there are small shoots showing low down then you can prune back to them. Or if you are really desperate...take a deep breath and a sharp saw!! I would only go back down to 3 or 4 feet though.

I 'd do the same as volunteer. deep breath and go for it.

But wait until this very cold weather is over....or is it too late?