You can trim to shape annually after flowering, cut out any dead wood in late spring, it's pruning group 8, Derek.

If you leave it too late in the season the the shoots might not have time to toughen up for winter. You can be drastic if you want to but if so I'd do it over two years to be on the safe side, perhaps let one half recover and shoot again before doing the other. I'm doing mine over three, and have just one branch to go next year.