Hi @joss,
You can use an icon from FontAwesome (see https://fontawesome.com/v4.7.0/icons/) as they are included in the theme. For instance, replace the current icon with <i class="fa fa-bell"></i>
to display the FA bell icon. (Please also see attached.)
So, these HTML markups:
<span class="menu-image-title"><span class="icon-wrapper"><i class="fa fa-lock" aria-hidden="true"></i><span class="h5 d-block">Your Data are Safe</span></span></span>
have to become:
<span class="menu-image-title"><span class="icon-wrapper"><i class="fa fa-bell" aria-hidden="true"></i><span class="h5 d-block">Your Data are Safe</span></span></span>
For quick demo, please give a look to the following video tutorial: https://youtu.be/IUDVjGCPo4I
We hope this helps! ?
Cheers,