Scenario: you want to change (not reset) a user's password using the Sitefinity API, but all methods (UserManager.ChangePassword() and UserManager.ChangePasswordForUser()) require that you know and provide the old password as a parameter. That's not always possible, so this blog will show you how to do it.
The trick here is that you first need to *reset* the user's password using the UserManager.ResetPassword() method - it does not require knowing of the old password, it simply generates a new one and assigns it to the user. So, this method will give you the new password which you can then pass to the UserManager.ChangePassword() method as the existing one.