This master thesis covers re-engineering methods of legacy systems. Legacy system is an old system, which is hardly compliant with modern technologies and used only because it has become an integral part of organization business process support during the long period of its maintenance. These systems are large, monolithic and difficult to modify, and cost and risk of their replacement are difficult to predict. The science of software engineering offers an incremental modernization of information systems applying the re-engineering of legacy software. The main goal of software re-engineering is to transform the software in the way, it would become easier to understand, maintain and re-use, at the same time preserving its useful, time trusted functions. The main re-engineering methods are source code translation, reverse engineering and data re-engineering. This thesis covers the analysis of these methods, which was made during the re-engineering of wood production and sales accounting system. The adoption and realization time rate of every method was examined. The influence of the applied re-engineering methods to the system reliability, efficiency, usability and other quality metrics is given.