Delete a Database User
You won't need the GUEST user account for this tutorial, so you can delete it. If you delete a database user account, the user will no longer be able to access any of the cluster databases.
Issue the following command to drop the GUEST user:
drop user guest;
The master user you created when you launched your cluster continues to have access to the database.
Amazon Redshift strongly recommends that you do not delete the master user.
For information about command options, see DROP USER in the SQL Reference.