Database server upgrades
If you have an earlier version of the Informix® database server installed, you must plan and prepare your system before you upgrade to a new major version or a fix pack of the same version.
The IBM® Informix Migration Guide explains how to plan for and perform the required prerequisite tasks for upgrading to a new version of the product, and how to apply fix packs and interim fixes. Review those topics carefully before you install the new software.