it's pretty much about text and context so you would talk about the differences and the similarities.
in terms of the change in values between frankenstein and blade runner, you would talk about a change in values due to a change in context
e.g. In bladerunner, there is an obvious shift from religious values, to those more relevant to the 20th century - the importance of economics - life itself has been commodified. Also, whereas in frankenstein, there is a clear warning against ambition and knowledge, in bladerunner, this has become warning against ignorance, to the fact that forms of life are important.
But I think the best way to go about this is to show that both texts reflect the same universal values but through different means and in response to two different world conditions.
Remember, just because a text portrays certain values doesn't necessarily mean it endorses them. So you can talk about the different sets of values portrayed in the two texts, contemporary to their time, but yet essentially they both endorse a similar set.