You must follow the instructions in the WebSphere Commerce Installation Guide to uninstall WebSphere Commerce and its components.
Uninstalling the software through the Add/Remove Programs utility
or by selecting Uninstall from the Start Menu will only partially uninstall the
software. This may prevent you from reinstalling the software, and you may
accidentally delete customized files. Uninstalling the software in the
incorrect order may also prevent you from using other components of the
WebSphere Commerce package, or prevent you from properly reinstalling the
software.