I suggest you wait until fall or even early spring. You can cut it back to keep the growth under control this summer but do not do any heavy pruning in the fall. An exception to this is if you have access to equipment that could dig under the root ball and transplant the vine to a new home with little disturbance of the roots. Find a new home with plenty of space....this clematis could cover the entire state of Montana with beautiful blooms each May. Keep growing, Marianne Binetti