To edit a swf file you will need the source code which is a .fla file which you can edit using macromedia flash. You can also use the SWF decompiler from Sothink. I don't know any software that does it for free.
Rjian The only way to get Macromedia Flash free would be to hack it. And of course that would be illegal, or you can get download it and then get the serial from an online serial site, wich ofcourse is illegal. Connor