It should be very easy to do in your subscription management area.

1. Either login normally or click here to get a magic link.

2. Use the button marked "Re-schedule" to select a future date for the subscription to process. Be aware, this is not the delivery date, it's the date the order will go through! Expect the order to arrive 3-5 days later.

Not sure when you want it? The "Delay" button gives you the option to delay by any number of days.