Replacing sash cords

Any Home Depot, Lowe's, window dealer, or lumber shop should be able to give you info you need. Why you would want to keep the weights I don't know. It's simpler to discard them. Cut the rope on them and remove the hardware. The'll drop in the well of the window unit. Unscrew the access near the bottom & remove them. Fill that cavity with insulation. Go to your hardware store, HD,L's,etc and get replacement friction guides. They slip into the same space and clip onto the bottom of the window. Before you re-install the trim, get a load of that "rope" type black sponge-filled insulation. It comes with self sticking flanges. Mount it under the guides & behind the window trim. Make it snug but not tight. Then re-install the window trim.