how could i get back my user name and password?

edit

Every log in password is associated to an email address.. you can search your email for the username or password (or possibly request for a new password maybe)

If you are trying to access your account on SageMathCloud at https://cloud.sagemath.com, click on "Forgot password?" at the top of that page.

If you are talking about access to the Sage Notebook for the version of Sage installed on your computer, see this ask-sage question.

Simply type

notebook(reset=True)

A new password will be requested to you.