Hi,
Go in the menu Products>Products to get a listing of your products.
There, click on the category "stranded silk" on the left explorer so you'll see the products of that category.
There, you'll see a column "order", with the ordering of the products in that category.
Then, go in your Joomla menu manager and edit the menu item with the alias "product-categories" which is the one used on your example URL.
There, under the "products options" tab, you'll find the "ordering column" and "ordering direction" settings.
These define what information of the products needs to be taken into account for the ordering of the products on the listings of that menu item.
If you have "ordering" selected in the "ordering column", then the system will use the values you have in the "order" column of the products listing that I was referring to in the first part of my message.
If you want your products to be automatically sorted alphabetically regardless of the value in the order column, you can select "product_name" in the "ordering column" setting.
The "ordering direction" setting will allow you to reverse the ordering.