Use a scraper to remove all old paint from all frames. Fill all small cracks with wood putty. It will dry out after a couple of hours. Level the surface of the frames with sandpaper. It may seem surprising, but sometimes when painting, you will need construction fittings.
Then, first with a vacuum cleaner, and then with a damp cloth, remove all the dust formed during the work. Using a special jelly-like primer, treat the entire surface of the frames. And then the frames will become perfectly even and smooth, and it will be much easier to paint them.
After two days, all metal parts must be treated with a special primer that protects against corrosion.
The entire surface must be thoroughly cleaned of hairs, particles of debris and dust. Otherwise, all these small particles can spoil the result after painting. It is also necessary to repair the window even before painting.
Glass, retreating a couple of millimeters from the edge of the frame, must be pasted over with strips of masking tape. Then the paint will be able to fill all the gaps between the glass and frames.
Outside, the frame must be treated with an antiseptic and painted with acrylic paint. And then paint the frame from the inside with alkyd paint, in which oil is added. And remove the masking tape.