Movement Script in C# for Unity

Move.cs

private float speed = 2.0f;
public GameObject character;

void Update () {
		
		if (Input.GetKey(KeyCode.RightArrow)){
			transform.position += Vector3.right * speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.LeftArrow)){
			transform.position += Vector3.left* speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.UpArrow)){
			transform.position += Vector3.forward * speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.DownArrow)){
			transform.position += Vector3.back* speed * Time.deltaTime;
		}
	}

not working using UnityEngine;

public class Move_ : MonoBehaviour
{
// Start is called once before the first execution of Update after the MonoBehaviour is created
void Start()
private float speed = 2.0f;
public GameObject character;
{

}

// Update is called once per frame
void Update () {
	
	if (Input.GetKeyDown(KeyCode.RightArrow)){
		transform.position += Vector3.right * speed * Time.deltaTime;
	}
	if (Input.GetKeyDown(KeyCode.LeftArrow)){
		transform.position += Vector3.left* speed * Time.deltaTime;
	}
	if (Input.GetKeyDown(KeyCode.UpArrow)){
		transform.position += Vector3.forward * speed * Time.deltaTime;
	}
	if (Input.GetKeyDown(KeyCode.DownArrow)){
		transform.position += Vector3.back* speed * Time.deltaTime;
	}
}

}