The aim of this thesis is to upgrade a version control system. The goal of the upgrade is to compare versions of files stored in a structured format. Some of the key functionalities of version control systems, development of systems over time and basic groups are described. The thesis contains step by step explanation and practical examples of OpenDocument Text file comparison. The process that compares textual part of document is explained for starter. Later, text formatting is also included in compare process. Thesis also includes an example of how very simple it is to use your own program for file comparing with version control systems.