Customizing themes
After you choose a theme that defines the basic look and feel of your online store, you can use the theme editor in your Shopify admin to customize the theme to suit your unique brand. With the theme editor, you can preview your theme, make changes to your theme settings, and add, remove, edit, and rearrange content. For more information about which sections and settings are available for your theme, check your theme's architecture version and the available customization options in the theme editor.
If your theme doesn't include settings for the changes that you want to make, and you're comfortable with HTML, CSS, and Liquid, then you can edit your theme code.