A hex editor displays a computer file as hexadecimal code, which is numbers in base 16 (normal decimal code uses base 10). So 0-9 decimal represent 0-9 hex, and 10=A, 11=B, and so on until F=15 and 10=16. So FF hex = 255 decimal. Before you start out, you need to know what characters the hex figures represent; two of the place you can look are http://www.csgnetwork.com/asciiset.html>here for the control characters and here for the rest.Using a hex editor, you can change any single unit in your file. It's an extremely powerful editing tool. But like any other tool of this power, user-friendly it ain't, and there is no quicker way of screwing a file up beyond all recognition if you get it wrong. So you ALWAYS make a backup before you start. Not sometimes, not even most of the time, but always.
There are plenty of hex editors available on the 'net as free downloads.
