i`m not a flash fan.. at all..
but, normally, if you don`t have the .fla, you can`t edit it
you won`t be able to edit a .swf file, ever
there are though some things called swf decompiler... some do a better job then others, i haven`t really tried any cuz i just dislike flash alot... bit you can go google for "swf decompiler" or "swf to fla"
these sofwares will convert your swf to a .fla.. and there you go...
many don`t really do the job well, as i heard, and you`llend up with a pretty crewed up .fla... but it is still more than a .swf to start from
good luck!