Knock Out roses really do not need standard rose pruning. To promote healthy growth and encourage lots of flowers, in late winter (or, now), simply use hedge trimmers or loppers to shear the shrub down to about 1/3 or 1/2 its current height. It is okay if what remains is only about 12 to 18 inches above the ground. This should help. If you are using pruners, try to cut back to an outward-facing dormant bud, because a branch will emerge where that leads away from the center of the plant.