Click 'Uninstall Ignite PI" from the "start/Ignite PI" menu folder.  Check to be sure the "Ignite PI Server" service was removed.  Sometimes the installer will leave it and it must be removed manually.  To remove it manually run the script:  c:\program files\confio\ignite PI\IgnitePI_RemoveService.vbs.  You can also delete that directory when the service has been removed.