How to stop JSON.parse() from changing contents?

Question

I'm using JavaScript to update the contents of a JSON file, I can successfully change the desired content and parsing it works fine, but it changes other values (and outright deletes others).

Ouput:

{ name: '8Hz', phones: [ [Object], [Object], [Object] ] },

Desired Output:

{ "name":   "8Hz",
  "phones": [
     {"name":"Salnotes Dioko","file":"7Hz Dioko","suffix":"7Hz Dioko"...},
     {"name":"Salnotes Zero","file":"7Hz Zero","preferredShop":"Linsoul"},
     {"name":"Timeless","file":["7Hz Timeless","7Hz Timeless (S2)"]...}
   ]
 },

Code:

const fs=require('fs');
var oldjson=JSON.stringify(require('./phone_book.json'));
var newjson=oldjson.replace('"name":"7Hz"','"name":"8Hz"'); //Replaces "7Hz" with "8Hz"
var final=JSON.parse(newjson);
console.log(final);