Why do you need a list? If you just want to destroy the bullets which are above some y coordinate, forget about the list and place this code in the bullet script:

void FixedUpdate(){
    if (rigidbody.position.y > 10){
        Destroy(gameObject);
    }
}

But if you really need to keep all bullets in some list for other reasons, just let Unity do that for you: create an empty object, reset its position to 0,0,0, name it "Bullets" and child all bullet instantiated to it:

  Transform bullets; // <- drag the "Bullets" empty object here
  ...
    if(Input.GetButtonDown("Fire1")){
       Rigidbody bulletClone;
       bulletClone = (Rigidbody)Instantiate(bullet, ship.transform.position + bulletCorrection, bullet.transform.rotation);
       bulletClone.velocity = transform.TransformDirection(Vector3.forward * bulletSpeed);
       bulletClone.parent = bullets; // bullet is child of "Bullets"
    }

Every destroyed bullet is automatically removed from the children list, thus you don't need to update it yourself. If you need to iterate through all bullets, use a foreach like this:

      foreach (Transform bullet in bullets){
          // do whatever you want with this bullet
      }

If you do want to use your own list, this works (I'm not a native C# programmer, so there may be a more standard way.) I used a LinkedList type just because. List is probably the same:

LinkedList<MovingText> L; // global

LinkedListNode<listType> nn = L.First;
while(nn != null ) {
  // Play with nn.Value:
  nn.Value.update();
  // grab reference to next, so we can safely delete:
  LinkedListNode<listType> nNext = nn.Next;
  if(nn.Value.isDead()) { // isDead is just my hand-written check
    L.Remove(nn);
  }
  nn = nNext;
}