"user": [
    {
        "name": "David",
        "currentProgram": "program1",
        "currentPhase": "C",
        "workout": [
            {
                "name": "Workoutname",
                "load": "10",
                "units": "kg"
            }
        ]
    },
    {
        "name": "Markus",
        "currentProgram": "program2",
        "currentPhase": "A",
        "workout": []
    }
]

"program": [
    {
        "name": "program1",
        "phases": [
            {
                "phase": "A",
                "cycle": [
                    {
                        "cycle": "day 1",
                        "exercises": [
                            {
                                "name": "workout1",
                                "set": 4,
                                "repetitions": 8
                            },
                            {
                                "name": "workout2",
                                "set": 4,
                                "repetitions": 8
                            }
                        ]
                    }
                ]
            }
        ]
    }
]

var user = require('./user.json');

user.get("David").currentProgram = "program2";
user.get("David").currentPhase = "A";

console.log(user.get("David"));