If you have placed your order and would like to add to it or change it before it has been processed, not a problem, head over to the Metro Hobbies Support Centre and select "I would like to cancel / change my order" and fill out the required details.
Unfortunately if your order has already been processed and packed you will not be able to add to it.
Please note adding to your order may cause a delay as your order will need to go back out for picking.