Go to SuperSu ( I assume you have it as the default super user app) .
Now install clockwork mods superuser app.
Then go to SuperSu, then click settings tabs, scroll down, find 'change superuser app' , click it, a pop up will come, read that and click okay.
Now SuperSu will uninstall.
then go to Superuser app.
it will prompt you to update binary.
installation success dialog will come.
now superuser will be the default app!
//Hit the Thanks button if I have helped you!