Show image in div and add PREV/NEXT buttons

This is untested – but might help you get the idea.

HTML

<div class="nextSelector">
    <span>NEXT</span>
</div>

JS

$('.nextSelector').on('click',function(){
    var nextImage = $('img.fullImage + img');
    $('img.fullImage').toggleClass("thumb fullImage");
    nextImage.toggleClass("thumb fullImage");
})