iCloud accounts include 5GB of free storage and additional capacity may be purchased at any time.
From the home screen, tap Settings.
Scroll to and tap iCloud.
Scroll to and tap Storage & Backup.
Tap Buy More Storage.
Tap an upgrade option, then tap Buy.
When prompted, enter the Apple ID Password, then tap OK.
Note: If prompted to confirm or add payment information, tap Continue and follow the prompts to add payment information to the Apple ID account.
iPhone storage has now been upgraded.