Editing score betwen scripts?

Hi I have 2 script:

 using UnityEngine;
 using System.Collections;
 
 public class _GameManager : MonoBehaviour {
     
     static int lifes= 3;
 public GUISkin guiSkin;
 
     void Awake() {
         DontDestroyOnLoad(transform.gameObject);
         
     }
     
 void  OnGUI (){
     GUI.skin = guiSkin;
     GUI.Label( new Rect((Screen.width / 2) - 60,10, 200, 30), "Lifes: " + lifes);
 
 }
 
 }

and:

 using UnityEngine;
 using System.Collections;
 
 public class ZlaOdpowiedz : MonoBehaviour {
 
 
     
     void OnTriggerEnter(Collider other)
     {
         _GameManager.lifes -= 1;
         Destroy(other.gameObject);
         Application.LoadLevel(1);
     }
 }

I think you see what Im trying to do... I get error and I cant repair it, someone can help me?

• wanna to make "if (lifes == 0){ Application.LoadLevel (1); } or somethink like thet

Thanks anyway ;)