Hi, Sergio. Fixing your windows can be very easy or really tough, depending on how much paint is holding the wood parts together. The first thing to do is take a knife with a thin blade and score the paint between the casing and the parting stop. The parting stop is the strip of wood that holds the inner window in place and you want to score the paint so it does not chip or peel when you pull the parting stop out.
Removing the parting stops (one on each side) is the next step. Hopefully this can be carefully pried out with a thin bladed screwdriver or stiff putty knife, but it sounds like it is really painted in place. All I can suggest is that you get it out the best way you can. You will probably break it but you can buy a replacement at most home centers in the millwork department.
When the parting bead is out, you can then remove the inner window. The rope will still be on the top of the window, probably held in with a knot held in a round recess, and probably one small brad. Remove the rope. Then remove the next parting stop and the outer window the same way you did for the inner one.
On both sides of the casing you will see a panel held in place with one screw. Remove the panel and the screw. Now you will see two cast iron weights on each side with a rope tied tied to the top of each. Now you can replace the rope (braided cotton clothesline works best) and replace the windows and parting stops.
Hope you could figure out these general directions. Some windows do vary slightly but should still be pretty close to this description of the process. Good luck. Henry in MI