JSON usuwanie danych Opcje

[lukaskolista]

Witam. Mam taki oto obiekt JSON

[PHP] pobierz, plaintext 
{"nextId":3,"data":[
{"id":1,"userName":"lukaskolista","content":"1","time":"2010-10-03 21:08:45"},
{"id":2,"userName":"lukaskolista","content":"2","time":"2010-10-03 21:08:48"}
]}
[PHP] pobierz, plaintext 

pobieram go nastepujaco

[PHP] pobierz, plaintext 
$file = file_get_contents('json.txt');
$json = json_decode($file);
[PHP] pobierz, plaintext 

jak usunac z niego 1 element tablicy data?