My SIR had done the same thing and grew to at least 7 ft tall. I have cut it back to be more manageable and watered good and it seems to be coming back well. I think I pruned it to about 5 ft.

Since fall and winter are coming soon you may want to wait until Spring to decide what you want to prune off...

How tall is your rose bush?

I would say that this rose bush is about 4 feet tall. There is a basic base of thick brown old canes, from which radiate several new canes. Most of the new canes are thin and weak. Under the burden of several blossoms, they leaned low toward the ground. Those are not canes that should remain, in my opinion. There are about 2 decently strong canes that grew from the old brown base canes.

If your afraid of winter winds causing damage then cut a bit off.

But I'd wait until Spring to do any major pruning....