The previous/next navigation is in the More Projects area:

If you’d like to swap out that whole More Projects area for a more traditional navigation, you’ll need to first create a child theme, and then copy the file single-jetpack-portfolio.php into your child theme folder. You can then replace line 26:
<?php sketch_portfolio_pagination(); ?>
With a more traditional navigation. You can take a look at Illustratr for an example.
Thanks for the reply, Anyway to add next and back buttons / links next to the the image the user is looking at? On either side of them?
Hi there,
Here’s some CSS you can use to add labels just above each image:
/* Post Navigation Labels */
.previous article:before {
content: 'previous';
}
.current article:before {
content: 'current';
}
.next article:before {
content: 'next';
}
You can add that to your site from the Customize > Additional CSS area.
Adding labels to either side might be possible, but it’s likely a bit more complex.
The text in the code above can be tweaked in terms of color, font size, etc, so if you’d like to use it and need help making those kinds of adjustments, just let me know.