Kill It With Fire is a good book about legacy software modernization. It has many practical advice, examples, and suggestions. I think it is missing something, but I am unsure what. I would have liked it to go more in-depth, more in practice, and more in the software part. Instead, as Bellotti says, the modernization of legacy systems is a people challenge, not a software challenge. You need to manage people, manage expectations, and keep up the momentum and the morale of the developers and managers.