If you’d like to use the official logos downloaded from:
Facebook: https://www.facebookbrand.com/
Twitter: https://twitter.com/logo
LinkedIn: https://developer.linkedin.com/documents/branding-guidelines
Google+: https://www.google.com/+/business/brand-guidelines.html
You’ll either need to:
1. If you’re using the free theme, setup a child theme and edit header.php:
https://startupwp.com/topic/child-theming/
OR
2. If you’re using the pro theme, setup the icons via your theme options as instructed under Appearance > StartupPro Options.
We can instruct further if needed.