[web2py] how to update auth_user first_name last_name programmatically?

[Constantine Vasil]

I want to change auth_user first_name and last name
progrmmaically having the user id:

I tried this:
        db.auth_user[id] = dict(first_name=first_name)
        db.auth_user[id] = dict(last_name=last_name)

but when reaching this statement in my db.py file I don't see 
auth updated:

    db = DAL('google:datastore')
    auth = Auth(db, hmac_key=Auth.get_or_create_key()) 

How is the right way to do that?