Hi megieswin,
The theme doesn’t support this, but you can do it by replacing existing built-in social media links with the one you like more.
Example:
Here is the image file for the facebook icon: https://demo.onedesigns.com/pinboard/wp-content/themes/pinboard/images/facebook.png
After creating a new .png icon, you name it “facebook.png”, upload it by FTP to the same directory (/pinboard/wp-content/themes/pinboard/images/) and use the facebook link provided within the theme to put your new URL instead of the link to your facebook page.
It is important to create a .png file in the same style as the hover is just pushing the png up and down to give it that sliding effect.
[ Signature moderated. Could you stop doing that please? ]