Hi alito1985,
Unfortunately this theme is quite different than the standard nopCommerce markup.
We downloaded the theme and tried to integrate the Ajax Filters plugin and found that there is some strange logic on some pages that is breaking some core functionality in nopcommerce.
There is a widget zone on the left column that needs to be show and the Ajax Filters are integrated into this widget zone but the theme has a different markup and does not show this widget zone (don't see any reason for this change really).
So you need to manually add this widget zone on the left column to get the Ajax Filters to appear. But this is not all as the markup and css classes of the controls is also different i.e view per page, sort by etc. So these controls will not be ajaxified by the Ajax Filters plugin.
You can upgrade to nopCommerce 3.6 and use the new default clean theme that comes for free and is fully compatible with all our plugins. Also all our plugins will have styling for the new default clean. You can see the new theme demo
here.