They are site sensitive. Go to the sites of the corresponding password in
the dropdown list, then select that password from the list at the
appropriate site, hit delete on your keyboard, type in the new password and
press enter. You should receive a message asking if you wish to replace the
old password with this password, answer yes.
The other way to do this is to clear all passwords but then you will have no
remembered passwords and have to start over at all sites. In Internet
Explorer go to tools, select Internet Options, go to Content tab, click
AutoComplete and click Clear Passwords.