Currently on your commerce site, the "Shop by Category" dropdown menu and left hand navigation menu shown on the home page are sorted in alphabetical order by default. You also have the capability to sort the categories in the order of product count.
In this example, we have clicked into the "Hardware" category and we can see that the subcategories are listed in alphabetical order.
To update your category order, start by navigating to PIM in the operations portal.
Then, click "Filter Categories". In order to access and update “Filter Categories” you will need to be set up either as an “administrator” or a “superuser”, or have the roles of: “facetGroupView” and “facetGroupEdit”.
To update the category order, you will need to update the filter category "productCategoryNames" with the desired category order setting. Filter or search to find the filter category.
Look for the "Order Values By" column. In this example, you can see it is set for "nameAsNumber" which orders the categories alphabetically. Double click into the field to update the category order. You can see that there are three different options: "count", "nameAsNumber", or "categoryOrder".
Since we would like to order categories by product count we want to choose "count".
Once the category page is reloaded, you can see that the categories are now ordered by product count.