I think the approach suggested in 'Working effectively with Legacy Code' (https://www.oreilly.com/library/view/working-effectively-with/0131177052/ https://www.

I think the approach suggested in 'Working effectively with Legacy Code' (https://www.oreilly.com/library/view/working-effectively-with/0131177052/ https://www.oreilly.com/library/view/working-effectively-wit...) is the right one. It's all about testing, and the confidence to make changes. So buy the book, read it, apply the ideas.