Hi,
If you recently change the settings (it was 18 previously) you might still seeing the 18 in the website, but it will be because of the cache.
Once you manually change the "product per page" number from the drop down, it won't be 18 by default. Or delete the history (and cache)
For further guidance, here are screenshots from our DEMO page: It might help you to understand how to change things:
1- In the backend:
Attachment Pasted_Image_2_8_14__3_06_AM-6.png not found
2- in the front-end:
Attachment Pasted_Image_2_8_14__3_09_AM-4.png not found
Regards,
support