How to get the index of an element in a singly linked list?

See more:

C#

I have two classes:

SLList for methods (private SLElement _root)

SLElement for creating new elements for the list. (public int _value; public SLElement _next)

I have finished the add-method:

public void Add(int value)
{
  SLElement addNewElement = new SLElement();
  addNewElement._value = value;
  SLElement rootCopy = _root;
  _root = addNewElement;
  addNewElement._next = rootCopy;
  Console.WriteLine(addNewElement._value);
}

So now I want a remove-function. I already got it working that it removes an element with a specific value, but I want it so that it removes an element with an specific index. How can I find out the index of the elements in my list?