If you're not going to be available for your original collection date, you can reschedule the collection to take place at a more convenient time from My Account.
Find the order number and click on "re-book a courier". You'll then be given the list of available dates to choose from.
If you'd like to arrange for the collection to take place at a different address, click "edit" next to your original collection address and fill in the new collection address details.
Once you've finished changing your collection preferences, click "submit" and a pop up window will confirm that your collection details have been successfully updated.