How to directly use Update Passowrd UI instead of the whole Preferences UI in Portal?

I know we can update user password through Preferences-->Password in portal.

But our client don't want to expose all the functionalities in Preferences UI, they only want set Password.

first question is how to customize the Preferences UI to only display Password link;

second, if cannot customize, and I need to write my own taskflow, what internal API I can call to update the password.

Thanks,

Wei