Modify Shopify Platform digital store. Only three products; want to replace videos and make minor modifications

I am an author. I have three self published books that I sell online through a Shopify hosted website. I have recorded four professional videos that I would like to replace the four videos currently on my site. If a consultant has knowledge and experience coupling a Facebook/Google advertising campaign with a Shopify store this could lead to a larger gig. I need help with both.