Deleting password information
If Safari is set to automatically fill in user names and passwords for you, you can turn off this feature and delete any user names and passwords Safari has stored.
To turn off AutoFill and delete saved user names and passwords:
Choose Action menu > Preferences and click AutoFill. (The Action menu is near the upper-right corner of the Safari window, and looks like a gear.)
Deselect the “User names and passwords” checkbox, and then click the Edit button next to it.
Select individual user names and click Remove, or click Remove All.
Passwords are not shown, but if you remove a user name from the list, its password is also removed.