Let suppose in your store there is a category called Tops and under that a subcategory called Jackets. You want to change the order/layout of the products in Jackets category on the front end.
To do so, select the category Jackets and then click on Manage Product Position tab, a pop up window Manage Catalog Positions with the products of the selected category will be available.
This is the current layout of the products on the website.
To change this layout, simply click on the product drag and drop the product to the desired location.
Once all the changes are been done, click on SAVE.
Refresh the page on the frontend to view the latest changes made.