How can I update a json element in postgresql json datatype

I can't figure how can I update an element in a postgresql 9.3 datatype.

My exemple the db

CREATE TABLE "user"
(
  id uuid NOT NULL,
  password character varying(255),
  profiles json,
  gender integer NOT NULL DEFAULT 0,
  created timestamp with time zone,
  connected timestamp with time zone,
  modified timestamp with time zone,
  active integer NOT NULL DEFAULT 1,
  settings json,
  seo character varying(255) NOT NULL,
  CONSTRAINT id_1 PRIMARY KEY (id)
)
WITH (
  OIDS=TRUE
);
ALTER TABLE "user"
  OWNER TO postgres;

The json part in "profiles"

{
    "Facebook": {
        "identifier": "xxxxxxxxxxx",
        "profileURL": "none",
        "webSiteURL": "none",
        "photoURL": "none",
        "displayName": "test2 test2",
        "description": "none",
        "firstName": "test2",
        "lastName": "test2",
        "gender": 2,
        "language": "none",
        "age": "none",
        "birthDay": "none",
        "birthMonth": "none",
        "birthYear": "none",
        "email": "[email protected]",
        "emailVerified": "none",
        "Added": null,
        "phone": "none",
        "address": "none",
        "country": "none",
        "region": "none",
        "city": "none",
        "zip": "none"
    },
    "Google": {
        "identifier": "xxxxxxxxxxxxxxxxxxxxxx",
        "profileURL": "none",
        "webSiteURL": "none",
        "photoURL": "none",
        "displayName": "test2 test2",
        "description": "none",
        "firstName": "test2",
        "lastName": "test2",
        "gender": 2,
        "language": "none",
        "age": "none",
        "birthDay": "none",
        "birthMonth": "none",
        "birthYear": "none",
        "email": "[email protected]",
        "emailVerified": "none",
        "Added": null,
        "phone": "none",
        "address": "none",
        "country": "none",
        "region": "none",
        "city": "none",
        "zip": "none"
    }
}

I'm using x-edit for the frontend, and I was hoping that something like that would work, but it doesn't.

UPDATE public.user SET "profiles"->'Facebook'->'social'->'facebook' = 'test' WHERE` id='id'

I can't seem to find any information on how to update a json datatype. Thanks for any help you could give me