I have a json file that looks like this: 

```
{
 "@id": "2",
 "@samsid": "d7058536c89b46c0b58117eff64372f7",
 "@productname": "Another paid for",
 "@downloaddate": "2013-05-28 11:37:12Z",
 "@downloadlocation":
    "2AFoGZVJpFHzspQD9UoE2C4VFYc8idiO4ebaRx4uEvtG+79DjkOUjJQjp9lJdSk54KIbFqzr",
 "@upgradeavailable": "2wECEpVJpFHS",
 "@downlaodstatus": "3QGf15VJpFFrUzr6oxwoew=="
}

```

I want to update the value of the attribute `@id` eg (`@id:2` To `@id:4`).

How would I do this?