Westpac have finally changed their password requirements allowing for longer passwords. My wife got a notice to change her password when she logged in today. I did not. I couldn't find any news or notice about it at all. I had to manually change the password by clicking on "Forgot customer ID or password" at the login screen. Yes, this does seem to be the only way. You don't seem to be able to change the password after you've logged in.
I don't remember all of the password requirement details but you can go all the way up to 30 characters including special characters. I just did a random 30 character password via my password manager and it was accepted.
Edit: I found where you change your password after you log in. It's in Service -> Preferences -> Security.
When I googled, Westpac help sent me to the method I first stated.
Sorry? I didn't say that my new password wasn't working. My new 30 character password is working. Westpac's change password method is just very strange.