This document discusses engagement models, upgrade principles, and considerations for upgrading a CRM system. It outlines guidelines for an in-place upgrade versus a side-by-side upgrade/rebuild. An in-place upgrade is recommended if the data is trusted, requirements are the same, the solution is native, the current version is within one of the target, and there are no integration changes. A side-by-side upgrade is recommended if new features replace old functionality, requirements have changed, the environment differs, the current version is more than one behind, or the solution is highly customized. It compares the timeframes of each approach.