Am I supposed to have windows live mail and outlook too??

I have outlook and I have windows live... which one do I need? I thought that windows live changed to outlook but I see that I am having trouble with an erros message at times when I try to email from outlook (delta server, message did not send) but the mails do send. And when I go to windows live I see I have many emails still on it that I had deleted from outlook. I would appreciate if someone can tell me what to do to clear this up. I am tempted to just delete windows live program all together but not sure if this is what I should do. Thanks