the best way to add / update a property / predicate

[scenaristeur]

Hi, nice lib, but should be updated( see my pull req on levelgraph levelgraph/levelgraph#196)

let's say i have inserted to the db something like

var manu = {
  "@context": {
    "@vocab": "http://xmlns.com/foaf/0.1/",
    "homepage": { "@type": "@id" },
    "knows": { "@type": "@id" },
    "based_near": { "@type": "@id" }
  },
  "@id": "http://manu.sporny.org#person",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "knows": [{
    "@id": "https://my-profile.eu/people/deiu/card#me",
    "name": "Andrei Vlad Sambra",
    "based_near": "http://dbpedia.org/resource/Paris"
  }, {
    "@id": "http://melvincarvalho.com/#me",
    "name": "Melvin Carvalho",
    "based_near": "http://dbpedia.org/resource/Honolulu"
  }, {
    "@id": "http://bblfish.net/people/henry/card#me",
    "name": "Henry Story",
    "based_near": "http://dbpedia.org/resource/Paris"
  }, {
    "@id": "http://presbrey.mit.edu/foaf#presbrey",
    "name": "Joe Presbrey",
    "based_near": "http://dbpedia.org/resource/Cambridge"
  }]
};
```

what is the best way to add /update a key, like for example add a new foaf:knows or update the @id of one already present ? 
Do i have to deal in jsonld / put for overwriting the existing one, should i get deal with subject/predicate/object ? or should i delete the manu object and recreate it with the updated properties ?