To enable swatches to your products, please go into your products in the backend of Shopify. When you get to your products, to allow alternating images, they have to be set for each variant, ( like the image above).
Then when you go into your theme, click on product template, it will lead you to the product page.
On the right left side bar, you have will a section called product template. When you click on the product section, you will get a right side bar of settings.
Under the product form, you can enable or disable the product swatches. If they are disabled, it will look like this.