// line read from the file
String line;

/* now input  */
// Name of the input file
String myFileName = ...;
// stream for reading from file
BufferedReader in = new BufferedReader(new FileReader(myFileName));

/* now output-stuff */
BufferedWriter out = new BufferedWriter(new FileWriter(myFileName + ".tmp"));


// readfirst line of the file, we don't care...
line = in.readLine();

// just make sure that the file is NOT empty
if(line == null)
    return;

// now copy the rest of the file
while((line = in.readLine()) != null)
{
   out.write(line, 0, line.length());
   out.newLine();
}

// close streams, perhaps in a finally block
in.close();
out.close();

// now the file without the first line has the extension .tmp

// you have to rename it. make use of File.renameTo() and File.delete();

// of course this code-block is NOT ready for use.
// you've to catch millions of exceptions and so on....