Change nav arrows

You would need to remove the background image and then use the :before pseudo class on the two navs.

Here’s an example using HTML Unicode icons. Using FontAwesome would be the same idea but you would include the FA Unicode and font-family. In either case, you may need to adjust the position of them.

.bne-testimonial-slider.bne-flexslider .flex-direction-nav .flex-prev,
.bne-testimonial-slider.bne-flexslider .flex-direction-nav .flex-next { 
    background:none !important;
}
.bne-testimonial-slider.bne-flexslider .flex-direction-nav .flex-prev:before,
.bne-testimonial-slider.bne-flexslider .flex-direction-nav .flex-next:before {
    content: "☜";
    color: #000;
    font-size:30px;
    top: -15px;
    left: -20px;
    display: block;
    position: absolute;
    text-indent: 0;
}
.bne-testimonial-slider.bne-flexslider .flex-direction-nav .flex-next:before {
   content: "☞";
    left: -5px;
}