我有一个json：

{
"pType": "1",
"pTitle": "A Product",
"pProds": [{
    "formM": 1,
    "sDesc": "A Product",
    "lDesc": "A Product",
    "pColor": "#000000",
    "pSize": "L",
    "postage": "2",
    "quatity": 2,
    "aPrice": "2",
    "rPrice": "2",
    "Discounted": "2",
    "Price": "2",
    "p_Num": "466ff237439a44be9d8fcc4725c28e4c",
    "images": [{
        "mN": 1,
        "idImage": "image1",
        "fileName": "39b06cc1aeb94e0c868d9b4e8174e2d5.jpeg",
        "bytes": "/img/ProdImages/466ff237439a44be9d8fcc4725c28e4c/39b06cc1aeb94e0c868d9b4e8174e2d5.jpeg"
    }]
}, {
    "formM": 0,
    "sDesc": "",
    "lDesc": "",
    "pColor": "",
    "pSize": "0",
    "postage": "0",
    "quatity": 0,
    "aPrice": "0",
    "rPrice": "0",
    "Discounted": "0",
    "Price": "0",
    "p_Num": "b8cf1caa638b48a2a3111b6d78c90b74",
    "images": []
}]
}

我想做的是用一个给定的id更新quantity（missspelled）值，这个id是p\num。
所以如果我需要通过p_num等于'466ff237439a44be9d8fcc4725c28e4c'将quantity从2更新到55
我该如何做到这一点？