How can I use Schema aggregateRating for the reviews on my website?

I have a third-party theme, one can review a property (real estate website) But the classes different than what it is needed for the Schema.

I need these in my website.

        <meta content="" itemprop="ratingValue" />
        <meta content="" itemprop="reviewCount" />
        <meta content="" itemprop="bestRating" />
        <meta content="" itemprop="worstRating" />

But mine is

<span class="review-rating" data-fontawesome data-path="http://ift.tt/28WBfhz" data-score="5" data-starOn="fa fa-star" data-starHalf="fa fa-star-half-o" data-starOff="fa fa-star-o"></span>

http://ift.tt/290aaxJ

via Chebli Mohamed