This can be done by several ways, if you can put your ladder up to the brickwork above the window whilst still keeping the correct ladder angle, you can usually clean it without problem, if there is no brick spacing above the window, you can put your ladder up to the guttering, make sure you've got some ladder mitts on the end. Usually you can reach the windows then as well. I have a tiny little unger extension handle, that gives you that extra little bit of reach.
If it's like a twin canopy, I don't know the right word, I'm not English, you know the sloping ends on both sides of the roof, you know what I mean, you can put the ladder up to the guttering as well, right next to the top of the roof, and then step over to the peak of the roof, that's usually quite narrow, but doable, grab the guttering, duck and clean the windows. Not the safest thing to do, but I bet everyone now and then has done that.
Safest way is an extension pole, might not do the perfect finish, but it beats a fall from a ladder.
Sorry, there is still another way for the twin canopy, you can put your ladders at an extreme angle, right across the roof from the side, rest the ladder mitts on the top, get a ladderm8rix at the bottom, and put your bucket on it as well to be safe, climb the ladder, and the window will be on your side to clean it.
Disclaimer
This is in no way allowed by health and safety, I'm just saying that it can be done, in my opinion it's safe enough, but you've got to be very careful.