Change Social media buttons in Theme's default widget

Okay I have found this code to be related to one of the icon’s in that widget.
<a href="https://www.google.com/+AjayGuptaIndia" target="_blank" class="social-icon" title="Follow me on Google+"><div class="icon icon-google-plus"></div></a>
Now I do not see link to any image file in this also in which .css or .php file will I find this code, can anybody help?
I found this code using Chrome developer tools.

I downloaded the theme offline & found a widget file & this code:

<ul class="social">
            <?php if($facebook) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Facebook','sugarspice') ?>"><div class="icon icon-facebook"></div></a></li>
<?php } ?>
            <?php if($twitter) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Twitter','sugarspice') ?>"><div class="icon icon-twitter"></div></a></li>
<?php } ?>
            <?php if($googleplus) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Google+','sugarspice') ?>"><div class="icon icon-google-plus"></div></a></li>
<?php } ?>
            <?php if($pinterest) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Pinterest','sugarspice') ?>"><div class="icon icon-pinterest"></div></a></li>
<?php } ?>
            <?php if($instagram) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Instagram','sugarspice') ?>"><div class="icon icon-instagram"></div></a></li>
<?php } ?>
            <?php if($youtube) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Subscribe to my YouTube channel','sugarspice') ?>"><div class="icon icon-youtube"></div></a></li>
<?php } ?>
            <?php if($flickr) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Follow me on Flickr','sugarspice') ?>"><div class="icon icon-flickr"></div></a></li>
<?php } ?>
            <?php if($rss) { ?>
<li><a>" target="_blank" class="social-icon" title="<?php esc_attr_e('Subscribe to my RSS feed','sugarspice') ?>"><div class="icon icon-rss"></div></a></li>
<?php } ?>

Now can plz somebody tell me how can i use custom facebook & twitter icons here.