Mergers and acquisitions (M&A) are frequently used tools for company growth. With M&A, companies can grow bigger and faster by creating a new organisation with more resources to achieve M&A goals. However, there are still ongoing discussions if M&A can achieve its stated goals and assure sustainable performance. One frequently mentioned reason for this is the inability to transform merging organisations. As information systems (IS) play an essential role in organisational architecture, the transformation of IS should take more attention in transformation planning and implementation. There are different possible strategies to transform existing IS; each brings specific value and requires particular circumstances to be realistic and efficient. This research focuses on the decision of a specific IS integration strategy for selected IS by applying a practical approach which evaluates each strategy from several perspectives - contribution to M&A goals, stakeholder support, user satisfaction, cost, risk and time. The process is verified by applying it practical case study.