My swf files are 800px by 500px. I would like to center them but the file always goes to left.
I think a more important question is why are you still using SWF files when most people can't see them?
In case you missed the memo, Flash is dead. The major browsers have already stopped supporting 3rd party plugins like Flash Player by default. And Adobe is ending Flash Player soon. You should be converting your Flash media to HTML5 Canvas or MP4 video.