The Helm app allows additional users to be removed at any time; these account changes can only be made through the Admin account.
The Admin account, created when you first setup your Helm Personal Server, cannot be deleted.
NOTE: Deleting a user from the account is a permanent action and cannot be undone. All associated information will be deleted and cannot be recovered.
To remove a user go to Menu > User Management > select the user. On that user's page will be an option to "Delete Account." Once tapped you will be prompted to confirm that you want to complete this action.