How to replace list item in best way

Question

if (listofelements.Contains(valueFieldValue.ToString()))
{
    listofelements[listofelements.IndexOf(valueFieldValue.ToString())] = value.ToString();
}

Answer 1

Following rokkuchan's answer, just a little upgrade:

List listOfStrings = new List {"abc", "123", "ghi"};

int index = listOfStrings.FindIndex(ind => ind.Equals("123"));
if (index > -1)
    listOfStrings[index] =  "def";