It is quick and easy to clean your VELUX roof window. To clean the outer pane, rotate the sash 180 degrees. The sash must be secured in position by sliding the barrel bolt into the bushing at the bottom of the side frame.
The air filter can be removed and washed with ordinary household cleaners. Fully rotate and secure the window in cleaning position, then remove the filter from the filter rail.
You'll find a complete guide to cleaning and maintenance of you window here