Login to your account. Enter details and click "Sign in".
Go to "Your Account".
"View / edit current orders", all open orders are displayed here.
Click on the appropriate order number 'button'.
Click on "Make changes to this order".
Click on "Continue".
Adjust quantities and make sure to refresh. Or to remove items, click the 'trash can' icon.
To add new items, click on "Continue shopping"
Add required items to basket as normal.
When happy with basket contents, click on "Checkout your order".
Add any comments as necessary and select your payment option. Click "Continue". To use the same payment card as the original order, select "Use the same payment as before". To use a different card, select "Pay by debit or credit card".
Continue to checkout your order following the normal procedure.