The document discusses the differences between upgrading and re-implementing Microsoft Dynamics NAV. Upgrading involves moving historical data and existing customizations to a new NAV version, while re-implementation only moves master and opening balance data and requires redeveloping customizations. The document outlines key factors to consider for each approach, such as the version upgrade path, database size, customizations, budget, and timelines. It then describes the methodologies for performing an upgrade, which includes code, report, and data upgrades followed by testing, or a hybrid approach combining elements of both upgrade and re-implementation.