It’s surprisingly easy actually… you just need to make sure you edit the theme in all the right places.

I used this resource here to guide me on how to best to achieve this: http://themeshaper.com/how-to-build-wp-pagenavi-into-your-wordpress-theme/

Code example after the link…

Just replace the existing navigation functions with this code, obviously after previously installing WP-Pagenavi first!

 

 

<?php if(function_exists(‘wp_pagenavi’)) { // if PageNavi is activated ?>
<?php wp_pagenavi(); // Use PageNavi ?>
<?php } else { // Otherwise, use traditional Navigation ?>
<div>
<!– next_post_link –>
</div>
<div>
<!– previous_post_link –>
</div>
<?php } // End if-else statement ?>
<br>