If you want to change the contents of a file (if it's a file), you need to rewrite the rest. There is no way of adding or deleting something in the middle of the file as it is a stream. So the basic algorithm is to read all before the text you want to discard, write it to a file (or just seek after the block) and then read the rest of the file (after the text you want to discard) and write it right after the first block.