Hey there Yolanda!
Eli here from the Shopify guru team. In this case, I'm happy to provide an answer somewhat simpler than the tutorial provided above :) The Shopify App Store has a "Variant Images" app that allows you to associate your images with the variants they represent, which can be installed for free: https://apps.shopify.com/variant-images
All the best, and let me know if there's anything else I can do.