You can't change the "like" icon, you can't touch the text. Basically you can't touch anything and can't modify nothing. This is what Facebook gives us.
But you can change where it is linked, so it would be "your own" Facebook like button. And start counting your own "likes".
Open the Joomla Module Manager and find this module:
"Footer"
and look at the HTML lines, you will find these lines;
<div class="fb-like" data-href="http://www.facebook.com/flexibleWD" data-send="false" data-width="200" data-show-faces="false" data-colorscheme="dark"> </div>
basically change the
www.facebook.com/flexibleWD with your own Facebook page URL and this Facebook Like button will be your own, and will reflect your own "like" numbers.
ALTERNATIVELY; you can generate your own Like Button from this URL:
developers.facebook.com/docs/plugins/like-button/
Regards,
Support.