Open footer.tpl form your current theme folder:

/templates/{current theme}/

Since it’s a basic HTML file, you can edit this file with any text editor.

Find in file the list-social-sites CSS selector.

You should be taken to the HTML responsible for your social links. It  should looks something like:

<li><a href="#"><i class="fa fa-facebook"></i></a></li>
<li><a href="#"><i class="fa fa-twitter"></i></a></li>
<li><a href="#"><i class="fa fa-youtube"></i></a></li>
<li><a href="#"><i class="fa fa-instagram"></i></a></li>

or

<li><i class="fa fa-facebook"></i> <a href="#">Facebook</a></li>
<li><i class="fa fa-twitter"></i> <a href="#">Twitter</a></li>
<li><i class="fa fa-youtube"></i> <a href="#">YouTube</a></li>
<li><i class="fa fa-instagram"></i> <a href="#">Instagram</a></li>

Replace # with your own social profile links.

Save changes and re-upload the modified file into your theme folder:

/templates/{current theme}/