I found the Q&A pretty close to what I want to know. (Even this, but I still not enough for me …)
http://wordpress.org/support/topic/how-to-make-changes-to-fancybox-javascript-values
I think in my case, I want to change the value of Available options (http://fancybox.net/api) as follows.
overlayOpacity: 0.7 (default 0.3)
showCloseButton false (default true)
showNavArrows false (default true)
titlePosition inside (default outside)
There are other, but I seem to be able to in the same way as the rest if I can change this.
I will certainly ask for advice to advance one step further.
Thank you.
