Your password and/or username can be stored on your computer, so that you don’t need to keep entering them yourself.
If you don’t want this, for instance if other people also use your computer or because you have changed your password, then you had better delete the stored details.
How you do this depends on which browser you use. If you are not sure which browser you use, you can check this here.
Via the following links, you will find an explanation per browser on how to manage stored login data (delete etc.):