Before you will add link in your template, make sure that users has correct permissions to change their passwords. Go to User accounts->Roles and policies edit user role and add new policy:
Module: user
Function: password Limitations: No limitations
From dropdown list choose your siteaccess name (usually public) and click set button, then create new override file. You can choose "Create as copy of default tpl ..." and edit original code in your new template. That's all, /user/password.tpl will be overrided now by your new tpl.