On the login page are you storing the id for the current user in a session variable? If you are using Security Assist this would be in the last page of the server behavior for Authenticate User.
With the session variable being set over here you just need to filter your recordset for the users on this variable when they go to the update page. On the current update page members_directory_Update_profile it looks like you are filtering the recordset on the URL parameter for id, you should update this to filter on the session variable from your Authenticate User server behavior or wherever the session variable comes from.