Storage is full

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

“Offloading” Apps can be a helpful method of creating temporary space for the software update.

https://9to5mac.com/2020/01/21/how-to-offload-apps-in-ios-to-save-space-without-deleting-their-data/

The only way you can create more storage space is to delete photos, messages, apps, etc.. Be sure to save important photos and data to your computer or an external drive. And be sure to restart the device after deletions. Check this link...

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