They mean almost the same thing, except that "having been" means definitely that you were instructed in the past. I can't say which I'd prefer-- "after being instructed to" is probably a little better, because in English we try to minimize the number of words we use when we write (and this is an entirely different argument-- you can watch native English speakers bite each other to death over "having been" vs. "being" and the passive voice and so on). But really either one is totally correct.