How can I re-order one of my previous orders (or re-order parts of it, or edit it for a new order)?

Make sure you are logged into your account on the website.  If you go into the  “Your Account” section on the website, and view your “ Order History,” there is a button next to each of the old orders that says “Copy to Cart” and it will copy your old order into the new cart.  Once it is all in the cart, you can edit it by changing quantities, deleting items, or adding new items to the cart.  You can then proceed to checkout as usual.