How do I make my walking animation transition to my running animation when I hold w and shift

My transition won’t work it just stays on walking animation when I hold shift and w I’m only 13 so this is a struggle for me. using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class running : MonoBehaviour {
public Animator animator;
private bool Running = false;

void Update()
{

    if (Input.GetKeyDown(KeyCode.LeftShift) && Input.GetKeyDown(KeyCode.W))
    {
        Running = true;
        animator.SetBool("isRunning", Running);
    }
    else if (Input.GetKeyUp(KeyCode.LeftShift) && Input.GetKeyUp(KeyCode.W))
    {
        Running = false;
        animator.SetBool("isRunning", Running);
    }

}

Input.GetKeyDown() / Input.GetKeyUp() only returns true on the frame it was pressed/released. If you you are holding down “W” key, then pressed “LeftShift” (or released), none of the code above will fire because the key presses did not happen on the same frame. Use Input.GetButton() as it stays true while it is pressed.

@jadd661 Well now when I stop holding down it does not go to idle