> It sems that when I update a download , that the
> HTTrack always overwrites all of the files .
> ? How do I prevent this , and just download only new
> or changed files ?

That is what it does. HTTrack needs to check to see if they are different,
that's why you all the files on the actions list.

If your seeing actual new downloads/replacement(the file dates are different)
then the files have changed. The most often/annoying cause of this is Ad
content. A different Ad on the same page  makes the page be
different/changed/newer.

But that should only apply to HTML content which is relatively small,  it
should not be re-downloading media content files (like .jpg) which tend to be
the bulk of the data.