The API-functions are available through the lightbox-object. It can be accessed through the elements data-attribute.

var lb = $('.bblb').eq(0).data('bbLightbox');

lb.toggle();
open
opens the lightbox
close
closes the lightbox
toggle
toggles the status of the lightbox
setSlide(el, slide)
change the content of a slide
el: can be object from API-mode or a jQuery/DOM-element
slide: can be empty for the active slide or an integer for the nth-slide (zero based)
showSlide(index, notransition)
show a specific slide
index: an integer for the nth-slide (zero based)
no transition: if true change without transition
nextSlide(notransition)
changes to the next slide
no transition: if true change without transition
prevSlide(notransition)
changes to the previous slide
no transition: if true change without transition
getSlides()
returns all slides of the lightbox
slides can be without content if they have not been preloaded