If you are unhappy with anything that you have purchased through a Brick Owl store, the first thing to do would be to contact the store. The store will try to resolve the issue with you. 

If an item is defective, you can return this for a full refund.

If you have changed your mind about something that you have purchased, and you wish to return it, the return policy will vary by store. The best thing to do is to contact the store to ask them if it's possible to return an order. Usually stores will not accept returns of parts orders, as they are picked to order.