How can I clean high roof gutters?
There comes a time when every do it yourselfer reaches the limit. In your case this may be yours. At some point the risk offsets the cost. Even with a forty foot ladder you will be working on the upper rungs. You will have a working range of a few feet on each side of the ladder. This means you will be moving the ladder 15 or 20 times. Unless you manhandle 40 foot ladders for a living it is a difficult and arduous task.  You may want to consider having the gutters evaluated. If you have large trees they may dropped leaves into you gutters. If they are clean now you may want to consider one of the many types of gutter- guard systems so they will stay clean.