If you need to add multiple items (for example add £5 to your total), as well as increasing the quantity on this page (click in the quantity box) you can just hit the ‘Payments’ button again, which will take you back a page and you can then add another amount: ‘Choose an option’ and ‘Add to basket’ and ‘View basket’ and it will bring you back to this page (Basket) and you can ‘Update the basket’ if you need to – to get a new Total (it should just automatically update). And when you are ready you can ‘Proceed to checkout’