You can't delete an open file. You need to CloseFile() first.
int fpNewFile;
// TO DO: assign a value to the string FileName
fpNewFile = OpenFile (FileName, VAL_READ_WRITE, VAL_OPEN_AS_IS,VAL_ASCII);
// TO DO: write data to file
CloseFile (fpNewFile);
// TO DO: do something with the file
DeleteFile (FileName);