Do you know if any of those stems are from the original cultivar? If one -is- (like maybe that smaller one that looks different?), now would be the season to cut ALL THE REST off! While it's dormant. Cutting it now won't sap energy from the new season's growth, and all you need do is make sure you don't introduce disease by cutting carelessly. (Most of all: use clean pruners. Very big cuts might benefit from extra protection, but I'm not an expert on this topic.) Best wishes!
