Hi Sergio, If you follow what Henry from Mi has wrote you will not be far out.so I'm not going to repeate what Henry has told you, but to go a little further along the line so to speak. I shall start from where you have taken out both windows ie: top and bottom sash's, "Very Important" DONT FALL OUT OF THE WINDOW. Keep that in mind at all times.( you will see what I mean later). The parting bead on both sides is now out, on the top left and right hand side you should have pullies two on the left, and two on the right. (Thats if both windows open and close) if only the top window opens then you will have only one on the and one on the right. Here we go.... now look at the left hand side of the frame, about 12" from the sill, you should see a little trap door (the groove for the parting bead runs through it,there maybe two nails nailed from the side thats holding it in place, also there will be another little door on the other side take that on out also, put the one on the left on the floor on the left, same with the other but on the right. Now you should see two weights or one weight( if one window opens only) take out the weights place them on the floor away from your feet ( we dont want you falling out of the window do we),make sure all the pullies are in good order if they are then carry on, next take a small amount of flat lead about 2"x2" roll this into a small tube,before you hammer it flat place the end of some parcel twine (string) tie a small knot on the end of the string, the push it up the lead tube, the string should be 5'-6' in lenght, now hammer the lead into a long thin rod holding the string, ( this is called a mouse). You will also need some rope about 3/8" thick good quality,(sashcord). Remember you have four pullies, two front rail/two in side rail. Take your mouse and bend it a little ( the lead part I mean) tie the other end to the sashcord, "This is the dont fall out of the window part" push the mouse into the front pully on the left, keep pushing the mouse till you see it in the trap door below, pull the mouse till you have the cord, cros over to the other front side "that will be on your right'" again push the mouse through the pully till you see the mouse again in the other door, keep pulling the cord so that the mouse can go through the inside pully on your left and do the same till you have a X across the window with the cord. Take off the mouse, and tie a weight to it, now pull the cord till the weight goes in side the door and up to the top where the pully is, put a nail through the cord about 8" down from the pully ( dont nail home leave the head so you can remove it later) cut the sashcord about 6" from the sill, now do the same with the other three.
In the window sash on both sides you should have a grove ( that where you will nail the cord to) Fix the top window first ( thats the one that goes out side channel ) make sure it's the right way round, you can some times have it the wrong way round "I've done it" nail 3 or 4 small nails in to the cord and then nail in to the grove, do the same on the other side, cut off the waste. with both side now done it should be easy to lift the window ( take out the nails on the top now) The top window should go up with no problem ? refix the parting bead on both sides after you have replaced the little doors that are on the left and right side of the frame. Now do the same with the bottom window which will be just as the top. ok. Replace the stop bead, that the bead on the inside and holds the inside window in place. " It should take 30-45mins per set of windows. and remember..