|On either side of the window frame you should see the panels that cover the weight pocket. Remove the screws that hold them in place. Remove the panels. Remove the weights and untie the old sash cords.
Tie a small weight to the end of a string and feed it through the pulley, dropping it down through the weight pocket opening. Tie a new piece of sash cord to the string and pull it from the top through the pulley. Tie the sash cord to the counter weight.
Set the window sash on the windowsill. Pull the sash cord so the weight is almost at the top of the pocket. Cut the sash cord about 3 inches below the notch that the knot locks into. Tie a knot at the end of the cord. Repeat this on the other side of the window frame.
If you are planning to replace the sash cords on the upper window, remove the upper window and install new sash cords by sliding the upper window down and then following the window removal and sash cord replacements steps above. Replace the upper sash now by setting it on the sill and wedging the sash cord knots into the notches on either side of the window. Reinstall the metal tracks using small nails or brads.