I need to add one number to the list of numbers

I have a json file in which I need to add one element, but each item there has its own number in order, so the problem is, how do I add +1 to each next number? I am aware I can choose multiple lines at once, but have no idea how to approach it. Each element looks like this. There’s about 200 of them, and I have to add a new element to the very beginning of the file. Any ideas?

"itemname" : {
  "order" : 170,
  "item" : "itemname"