iCloud Storage

iCloud storage is entirely independent and separate from your internal storage. Your internal storage is fixed at time of manufacture- and cannot be changed.

iCloud is used for offline “cloud” storage - for creating synchronised copies of your photos and other documents and data. Your iCloud backups are also stored here.

If you are unable to download Apps because you internal storage is full, you must delete data from your internal storage.

The physical storage capacity of your device has not changed and cannot be changed after purchase. What you subscribed to is storage in the cloud. Now, that you have off-device storage, however, there are a number of things you can do to reduce the storage needs of your device. See the article below for suggestions.

How to free up storage on iOS devices:

https://support.apple.com/en-us/HT203097