Storage full

How to check the storage on your iPhone, iPad, and iPod touch - https://support.apple.com/HT201656 - "If your device is low on storage, iOS automatically optimizes its available space while installing an app, updating iOS, downloading music, recording videos, and more."

If your internal storage is full, your only option is to better manage the storage that you have - and delete unused Apps or unneeded data.

These support pages should prove to be helpful:

What's the difference between device storage and iCloud storage? – Apple Support

Manage your iCloud storage – Apple Support

How to check the storage on your iPhone, iPad and iPod touch – Apple Support

Clear Other storage on your iPhone or iPad - Apple Support