This makes it real easy to replace old windows with the new insulated type. When replacing windows in a house that has the older double hung windows you may be able to leave the inside trim alone and do most of the work form the out side.
Many old windows use the weight and rope function.
If you are not going to be tearing the walls apart, then it is best to cut the rope and let the weight remain in the wall. Before you do any removing, you will need to measure the size of the replacement unit and get it ordered from the glass or window supplier. It will take at lease a couple of weeks or longer for them to build the windows. The plan is to keep the interior trim in tact and install the new window from the outside so it fits against the inside stop. T his will allow for caulking, shimming and an out of square opening.