I want to edit interface files, but I'm not sure of the tools I need to use, neither if there is some special editing I need to do to use those tools. I suppose I need to convert the swf files to fla format and then edit with flash or a similar tool, but I suppose there is something more involved here.

Do someone know how editing the interface works and if there is some kind of tutorial?

You could ask in the http://www.gamesas.com/topic/1333250-relz-skyui/, lots of people have been looking into the UI stuff there.

Thanks . Indeed another person asked it first there.

There were (before skyui released) massive threads titled "Modding the UI" and its where skyui first cropped up with screenchots. people were sharing how to do x and y etc.

http://www.gamesas.com/topic/1256213-interface-change-pc/
http://www.gamesas.com/topic/1267229-modding-the-gui/
http://www.gamesas.com/index.php?/topic/1275750-modding-the-gui/
http://www.gamesas.com/topic/1290652-modding-the-gui/