prestashop更改页面图标不起作用

I am using Prestashop for the first time. I try to change icons in the default theme but the change doesn't reflect on the UI

E.g: in block contact info, I have originally

<li>
          <i class="icon-phone"></i>{l s='Call us now:' mod='blockcontactinfos'}
                    <span>{$blockcontactinfos_phone|escape:'html':'UTF-8'}</span>
                </li>

I want to remove <i class="icon-phone"></i> and add my own icon <img src="\img\icons\call.png" />

But the UI still look the same after I changed the code to

<li>
                    <!--<i class="icon-phone"></i>-->
                    <img src="\img\icons\call.png" />{l s='Call us now:' mod='blockcontactinfos'}
                    <span>{$blockcontactinfos_phone|escape:'html':'UTF-8'}</span>
                </li>

I use chrome inspector and see that the source code doesn't change at all. How can I add my own icons in prestashop?