A clean uninstallation of capabilities is a necessary step for upgrade, and it may leave in the system specific objects that are useful for a later re-installation.
Uninstalling Content Manager Removal of all Content Manager items of the installed environment is required before starting an upgrade.
Uninstalling Content Delivery When you uninstall Content Delivery, the program files are removed, but application data (content, customized styles, skins, and delivery packages) remains in the application data path. If you intend to reinstall to the same path after uninstalling, move the application data to a different location (or delete it) before reinstalling.