Transitioning from WP Show Posts to GB Blocks?

I haven’t yet downloaded GB 1.5.0, but plan to do so soon to try it out - but as I have quite a few clients’ sites using WP Show Posts, I need to know what the transition process will entail, as WP Show Posts is phased out. IE: how do I update sites currently using WP Show Posts when the new version of GB is available for general use (ie: not beta or alpha)? What are the steps involved - and how time-consuming will this be?