转换为字符串，删除一些部分并转换回byte[]

我需要删除转换为字符串的字节[]的前4句。

目前为止我有什么:

//convert bytearray to string, so I can modify the string
string rawString = Convert.ToBase64String(rawByteArray);
//seperate lines
string[] textLines = Regex.Split(rawString, "'r'n");
//I need to substract the first 4 senctences of the string here!
//convert string back to byte array
byte[] cleanByteArray = rawstring.FromBase64String(rawString);

我如何减去前4句话?

提前感谢!

var newstr = String.Join(Environment.NewLine, Encoding.UTF8.GetString(buf)
                                .Split(new char[] { ''n', ''r' })
                                .Skip(4));
buf = Encoding.UTF8.GetBytes(newstr);