Best practice to modify some attribute value in a json string?

We are using SharePoint 2013 and Nintex workflow. In some workflow I do a webrequest which returns a json string. Inside this json string there are alot of attributes with their values. I would like to modify one of the attribute values. What is the best practice to do that?

This is an example of the json string:

{

"attribute_A": "2018-02-15T00:00:00+01:00",

"attribute_B": "2018-02-15T00:00:00+01:00",

"attribute_C": "abc",

"attribute_D": "1234"

}

I would like to set the value of attributes "attribute_A" and "attribute_B".