How to kill process client

If you mean how to kill client,
modify your server and client to make possible following:
- send by server some original string/command, that will be recognized by client as exitcommand, and then Close();
If you mean how to kill process by client, that(process) is running on server side
http://www.dreamincode.net/code/snippet1543.htm

How I done it some when:
- send by client string says "process?"
- server receiving this string creates process list, store they in Array
and transfer to client as striing, using, says, "?" or "\" as separator.
Client create this list and needed process was killed by sending its Array index.
So you need also Google for "process list C#".