How To Modify An Element in the Dictionary Class?

Question

How To Modify An Element in the Dictionary Class?
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C# has this cool Dictionary class that you can use like a Hash Table.  Is there a way of changing the value of an indexed element without resorting to removing it like this?
  int value = runningcount[city];
  runningcount.Remove(city);
  runningcount.Add(city, ++value);

and, by the way, how do I change my avatar here?