アセットの使用なし版

ChangeUISize.cs

public class ChangeUISize : MonoBehaviour {

    public GameObject panel;

	void Update () {

        if (Input.GetKey(KeyCode.Space))
        {                        
            StartCoroutine(ChangePaneltoBigSize());
        }
	}

    IEnumerator ChangePaneltoBigSize()
    {
        var size = 0f;
        var speed = 0.05f;
        
        while (size <= 1.0f)
        {
            panel.transform.localScale = Vector3.Lerp(new Vector3(0, 0, 0), new Vector3(1, 1, 1), size);
            size += speed;

            yield return null;
        }
    }
}