When upgrading SAP IQ on a Windows or Unix platform, be sure to uninstall the existing version before installing the new version. It is not recommended that you either install the new version over top of the existing installation or to a different folder on the same server. Failure to uninstall first could result in unexpected behavior running the new version.
On Windows, environment and registry settings are global, and are set by SAP IQ during installation. If you do not uninstall first, the existing SAP IQ environment and registry settings are automatically overwritten by the new version. Mixing settings and versions will result in errors. In addition, a new installation may introduce new settings while deprecating others. A new installation does not check for and remove deprecated settings. Failure to remove these settings could cause registry conflicts.
On Unix, if you have multiple versions installed, and you start an upgraded (newer) database with environment variables and binaries from different versions, you could encounter unexpected behavior or errors.
In short, uninstalling first guarantees a smooth upgrade process by ensuring all existing binaries, environment, and/or registry settings for the older version are removed before installing the new version.