You have to use the Poke' Bank which is approx. $5.99 a year how ever.
There is a 30 day trial (as long as you use it before the 1st of Feb).
This is from X and Y FAQ
What are the details of the trial period for Pokémon Bank?
If you download and open Pokémon Bank by January 31, 2014, you will be able to obtain a pass that will allow you to use the software for no charge for 30 days.
Before February 1, 2014, you will need to:
1. Download Pokémon Bank from the Nintendo eShop.
2. Open Pokémon Bank.
3. Follow the on-screen instructions to obtain your pass.
This pass unlocks a 30-day trial period. During this time, you will be able to use all of the features in both Pokémon Bank and Poké Transporter without charge.
If you download Pokémon Bank but do not open the software and obtain your pass by the end of January 31, 2014 (Friday), you will not be able to obtain the pass. Please be sure to take advantage of this opportunity while it lasts.