I want to learn to do alterations. How?

I just want to alter my ready-to-wear clothing. It’s surprisingly hard to find a book on this (as opposed to the many books out there for the home sewer on how to alter a pattern before sewing a new garment). Right now I have a lined jacket that I got at goodwill and I’m wiling to practice on it because it’s not valuable, but nicely made… too big in the shoulders and bust, though. How would one reduce existing bust darting? remove shoulder pads and fix sleeve/shoulder? deal with the existing lining? Help!