saving passwords

On a secure web site, whenever I open the page a drop down menu appears asking me if I want to save the log in information or not save it. I mistakenly clicked on save. I don't want to automatically open the web site with a click of the mouse. I want to enter my account information and enter my password each time. I don't know how to reverse my mistake and have the requirement to log in each time. (Out of curiosity, just where is the password data saved?)

Additionally. how can I avoid having that nuisance window from popping open each time I want to log in? It is an extra step I don't need to make to keep answering no every time I access the site.