Before you can delete a login, you must do the following for each user with which the login is associated:
Revoke the user’s command and object permissions with cascade. Revoking permissions with cascade revokes them from users to whom this user has granted them.
Re-grant the revoked permissions to the other users, if appropriate.
Delete objects owned by the user.
Delete the user from all databases.
Because of all the preconditions for deleting a login, you may want to lock the login instead. See “Locking a login”.
Only a system administrator can delete a login.
Deleting a login
Select the login icon.
Select Edit | Delete.
Confirm the deletion in the confirmation dialog box.