How to delete/uninstall SuperSU?
If installed via TWRP recovery, you can press the unroot button in SuperSU settings and then drag to remove.
If installed via Google Play, you can also drag to uninstall.
If you are using beta versions, which are named either BETA or SR#, their maybe some issue with uninstallation. Once the stable version is ready, you can update to stable version and follow the method above to uninstall the software.