A decision about introduction of an information system into a company is always connected to evaluation of its contributions to activities within the company. It is a very complex problem, because opinions of managers, IT experts and even common users within a company vary. Technical parameters, user requirements and financial intensity for implementation or change in the information system are ... [Show full abstract] main, but not the only criteria, which influence final decision-making. The aim of this article is to describe in practice used process of decision-making on implementation or change in corporate information system. The same process can be used in corporate practice to solve and valuate decision about extension by subsystem or partial information system changes.