how we can change and use a variable in different classes?,

I wanna to change a variable in a class and use it’s changes in other class.
what should I do?
tnx,

// Here simple example like that you can access easilly

public class AudioManager : MonoBehaviour {
	public static AudioManager instance;
	public int i;
	// Use this for initialization
	void Start () {
	   instance = this;
	}
}
// Other Class...

public class OtherClass : MonoBehaviour {

void Start () {
	  AudioManager.instance.i = 10;
	}

}