No worries at all, @Lowie57 !
Swapping out the social media icons for custom icons and adjusting their size will need coding customization to achieve. If you wish to use the icons you prepared, you can hire a Shopify Expert to help you add them via coding. Otherwise, you can use an app in your store for custom icons such as Social Media Icons or POWR Social Media Icons. Should you have questions about the apps, you can contact their support team under the Support section of their listing.