This group of clematis generally doesn't need much regular pruning, as it flowers on old wood, and if you prune you will lose next year's early flush of flowers.
If you need to prune to keep the plant in the space you have allotted to it then prune immediately after flowering to give the plant time to recover and put on growth in the summer. Remove dead or damaged stems, and once flowered, reduce other stems back to keep tidy.
For renovation, cut back harder to around 30cm from the base immediately after flowering.