You can update your Sounds subscription anytime by visiting:
When you upgrade you will be charged the price of the new subscription right away and will be issued all the credits immediately. This will also reset your billing cycle.
For example , if you are on the Sounds 100 and upgrade to the Sounds 300 you will be charged $13.99 and issued 300 credits immediately. Your billing cycle will reset to the date you upgraded.
When you downgrade you won't be charged, it will charge you the new subscription price on your renewal (this does not change your billing cycle).
For example, if you are on the Sounds 300 and you downgrade to the Sounds 100, no changes will occur until you hit your billing cycle date, at which you will be billed $7.99 and issued 100 credits.