FileStream fs = new FileStream("c:/something/somewhere/file.txt", FileMode.Open); //i don't know what you file is, it probably isn't this.
StreamReader sr = new StreamReader(fs);
string file = sr.ReadToEnd(); //'file' is your file...
file = file.SubString(1); //...only now it's missing the front
sr.Close();
fs = new FileStream("c:/something/somewhere/file.txt", FileMode.Create); //this will completely destroy your old file. harsh but fair.
StreamWriter sw = new StreamWriter(fs);
sw.WriteLine(file); //bingo.