Hi I needed to do something similar, I used this code below:
{def $active_user=fetch('user','current_user')}
{section show=$active_user.is_logged_in}
#Place your change pasword button here.
{section-else}
#Don't do anything here
{/section}
{undef}
Now if your user is logged in the button should appear, if not no button should be present. You may need to change the variable $active_user to suit, thats just the name I gave mine.
