CForms for Joomla! documentation
Uninstall CForms for Joomla
Please note the uninstaller does not delete the #__cforms* tables out of data security reasons. So you need to manually delete them to remove CForms completely or start from scratch.
You can uninstall CForms like any other Joomla! component. If you uninstall the Main component (just called CForms) all plugins, modules etc. are also uninstalled.
As a super administrator just navigate to Extensions -> Extension Manager -> Manage, than search for CForms, select it and click on uninstall.