The details shared here apply to the most recent version of our themes. To keep your theme up to date, check out this helpful document.
In all of our themes, you can enable a "hover to zoom" feature for your gallery images on your product page within the theme's settings.
For Parallax, Retina, Responsive, and Mobilia:
Head into Customize > Theme settings > Product grid. Under Product Gallery > Image Gallery, select the "hover to zoom" option.
For Turbo, Artisan and Flex:
Head into Customize > Select "Product Pages" from the drop-down selector. Under Sections > Product > Product Gallery, enable the "magnify product images on hover" option or "magnify on hover" setting.