Very simple example:
# retrieve
user_entry=apps_service.RetrieveUser(username)
# set new username
user_entry.login.user_name=new_username
# if new frist and last:
user_entry.name.given_name=new_givenname
user_entry.name.family_name=new_familyname
# update
apps_service.UpdateUser(username, user_entry)