Posted: 07/06/2017 at 22:01
It sounds like a group 2 which means a light pruning and a good feed of slow release clematis, rose or tomato after the first flush of flowers in May/June to promote a second flush later in summer.
I suggest you remove all the flower heads so it doesn't waste energy on the seeds and then take half of the stems back to just above the lowest 2 pairs of leaves. Leave the cut stems to wilt a week or so. It will make them easier to pull out from their base without damaging the remaining stems. Given a good feed and watreing during dry spells it should grow new stems which will flower lower down.
If that all sounds too complicated, dead head and feed anyway and then, next spring, cut it down to the lowest pair of buds on each stem and feed generously. It will grow a complete new set of stems you can train across the supports and then keep in bounds by training as it grows and gives you new flowering stems.