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Paying for Spotify through iTunes is 30% more expensive than doing so directly with Spotify.com because of Apple’s transactional costs.
Here’s how to switch your account to the lower Spotify.com rate:
Follow these steps to turn off future payments with Apple.
Wait until the month you already paid for ends. (See renewal date here.)
Note: Your account will remain on Premium during this time.
Then head to the Premium page. Log in when prompted.
Enter your payment details and click START MY SPOTIFY PREMIUM.
That's it! Your account is now switched to the lower Spotify.com price.