Compared to other types of windows, double hung windows are high maintenance; because you must slide up and down the two sashes until you manage to clean them properly; you may also need to support the windows with your hands, otherwise they may incur damage; alternatively, you can set a chair underneath the windows, with its back facing them for support.
In the center of the two sashes, there is a mechanism that you must turn counterclockwise to lose the grip and unlock the window. Identify the wash assist tabs (they should be located on each side of the frame, above the window sash). Slide the tabs until they are wedged down between the frame and the sash. Use both hands to grasp the lower sash and pull it towards yourself. It will tilt inwards, not before you feel a slight resistance. Keep tilting the sash (but not more than 90 degrees!) and support the glass with a back chair, or another durable object.
Slide the wash assist tabs back to the top of the frame, so you can lower the upper sash until you can reach the title wash tabs, on the top edge. Leave a space of at least one inch between the upper and lower sashes. Simultaneously move the assist tabs inward and pull the upper sash towards you, until it rests on the lower sash.
In this position, you can comfortably clean both sashes. See more on windows and window replacement solutions at https://www.dmdbuilders.com.