Apple notified all its former MobileMe customers Thursday that the complimentary service of 20 GB iCloud storage will expire September 30, 2013.

Apple Inc, one of the largest smartphone and PC makers, announced Thursday that all former MobileMe customers will be losing the complimentary iCloud storage service on September 30. Apple will automatically adjust the complimentary 20 GB storage to its free 5 GB plan.

Apple offered a complimentary storage plan for former MobileMe members after they moved to iCloud.  MobileMe was an Apple-supported software for online backup before it was shut down and replaced by iCloud in 2012. Apple offered a similar 20GB storage in the cloud if the former MobileMe customers renewed their subscriptions with iCloud.

Apple also announced that the customers will have an option to continue with the same storage for an additional $40 per year.

Apple has updated its Support Page with some frequently asked questions about the transition from 20 GB to 5 GB storage on iCloud, how to check what storage customers are using, how to upgrade, downgrade or purchase the current plan.

Apple will also be notifying all its former MobileMe customers via an email, a copy of which was obtained by Apple Insider that gives information about the upcoming transition.

"As a thank you for being a former MobileMe member, you received a 20 GB complimentary storage upgrade when you moved to iCloud," the email reads. "Your upgrade expires on September 30, 2013. When it expires, your iCloud storage will be automatically adjusted to the free 5 GB plan."