old stained window frames
Not really enough information from you to give you a useful answer. A picture of the windows in question would be hugely useful.
Are these old wooden window frames, painted, and the paint is stained and deteriorating? If so then scrape and sand, prime and then paint. How much scraping, sanding, and filling and/or repair all comes down to what sort of shape they are in. If the paint is old enough to include lead in it then you should read up on best practices for on safely dealing with it.