If you wish to add / remove a product or empty your basket, here's how to do it:
Start by clicking on your cart to access it.
To remove an item on the website : click on the little bin at the top right.
If you're using the app: there's a "-" sign next to the product to change the desired quantity.
The item will then be removed from your cart.
To add another product to your order, just start creating another additional product then click on "Add to cart". All you need to do is to place your order with these two products.
If you want to order multiple copies of the same product, add this product to your cart, then click on the drop-down list next to the product you just added and choose the desired quantity.
If you're using the app, you just need to click on the little "+" next to the product.