1 Answer

If your internet browser has saved other user's addresses and passwords in autofill, you can delete them through the browser's preferences.

In Safari: Open Safari. Go to the menu bar > Safari > Preferences > Autofill > click the Edit button for usernames and passwords. Delete what you don't want. 

In Firefox: go to a page where one of the autofill options is. Say, email log in page. Double click one of the text boxes filled with the unwanted email address/password. Highlight the option you want to remove (you'll need to do this one by one, manually). Now press the delete key on your keyboard (if that doesn't work, try pressing the delete key together with the Shift key).