Shop & Product Page Customization

Hello. I recall about a month ago being able to change the layout of my shop page in terms of number of products per row, column, etc. Now I can’t for the life of me figure out where to do that. Apparently when you’re on the shop page and you go into the “Customize” interface, a special Shop customization window should pop up with these options, but it isn’t coming up for reasons I’m unsure of. Do I need a paid theme extension to be able to access the shop & product page customization windows?