Add files to iCloud

Go to Settings > Apple ID > iCloud and toggle on the services you wish to sync to iCloud.

You may wish to optimize photo storage to save some space (Settings > photos)

Note that syncing your files will not remove them from your device and deleting any item on the iPad will also delete it from iCloud.

It is impossible to increase the amount of internal storage in your iPad - as this is fixed during manufacture; what you have is fixed for the life of your device.  You can, however, subscribe to a higher tier of iCloud storage - but this is not a substitute for internal storage.

You have a free iCloud 5GB Storage allowance; you can subscribe to higher tiers - 50GB, 200GB and 2TB:

Subscribe to iCloud+ on iPad – Apple Support

If your internal storage is full, your only option is to better manage the storage that you have. These support pages should prove to be helpful:

About storage on your device and in iCloud – Apple Support

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

Dcsend Said:

"Add files to iCloud: Storage on iPad is full. Can’t delete anymore. How do I add files to cloud"

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Remove from iTunes Library:

Just curious: Did you remove items from your iTunes Library? Movies and TV Shows can take up GBs of data. So, remove those, as they are usually unnecessary to have installed.