any chance you provide a bit more details?
at least which file exactly has to be edited..
the file is
Voting is done by getCommentVote function with is in line 166
Markup for the buttons starts at line 179
or can you suggest how to add different mark for Thumbs Up? for example
when someone votes Thumbs Up you get 3 points instead of 1.
I guess the easiest way to change weight of the positive votes would be by changing the resulting calculated value. The button hits will stay as they are, but they would be counted differently.
There is getCommentVoteValue function n line 189 and it has the calculation of the final voting result in it (line 191)
$value = intval($comment->isgood - $comment->ispoor);
As you see, there we have a simple subtraction of negative votes from positive ones. You can multiply the positive vote count by whatever number you want and thus give it a different weight. For example, as you asked for a multiple of 3,
$value = intval(($comment->isgood*3) - $comment->ispoor);
will make positive votes count three times as much as negative ones.
I hope it helps.