I can answer this here since this question is related to the free Site Reviews plugin. However, in future, please use the Support form on your Nifty Plugins account for any question related to the premium features of the addons.
If you are using the shortcode to display your reviews, use the display and pagination options to control how many reviews are displayed.
For example:
[site_reviews display="12" pagination="loadmore"]
To learn more, please read the included shortcode documentation page:
