Begin by selecting the delivery option that you would like to use, as well as inputting relevant delivery addresses and billing information. When happy, head to the review section of the checkout, where you can double check the information you have just input is correct. It is also in this section where you can enter your Parcelforce promo code. This is undertaken by copying and pasting the code into the promo code section, or by navigating a pop-up window. Once applied, you should see the subtotal now reflecting the discount associated with your promo code.