I was looking for a similar information and came across this question of yours. Actually I was trying to understand how was this "remembered password" stored, and if it was safely stored.
Then I stumbled into @Gilles answer to a similar question in Stack Exchange.
Based on that answer, you can go to "Show applications" -> "Passwords and keys". Your stored password should be found under "Login", and can be deleted.
Under the default configuration in Ubuntu, passwords are stored in the
GNOME keyring. This
applies to all passwords stored by Nautilus, as well as most other
applications including web browsers.
(Let me reiterate: default configuration, most. This can be
changed and there are applications that don't support the Gnome
You can use the Seahorse GUI
program or the
command line utility to view and modify the contents of the keyring.
There is some official documentation about Gnome
Keyring, including a
and a more concrete security
Data in memory (“Remember password until you logout”) is present in
the memory of the
gnome-keyring-daemon process, which allows any
process running as your user to query it. Gnome-keyring avoids
possible; however, if you have any encrypted storage, you should have
encrypted swap, because the programs that manipulate the confidential
data could themselves be swapped out.
Data on disk (“Remember forever”) is stored in the file
~/.gnome2/keyrings/login.keyring. It is
with a key that's derived from a password; normally, that's your login
password, and Ubuntu is set up to unlock the keyring with your login
password. The key
is derived from the password with a salted, slow
but I don't know exactly what the derivation function is.