iPad Memory

Other than offloading or replacing your iPad with a model with more internal storage, 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:

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

If you're using iCloud Photos sync, you didn't "moved" your photos/videos, you just synced them to iCloud, but they are still on your iPad too (so that if you delete one picture from your device, it will be deleted from iCloud too).

That said, if you need to make room on your device, you can take a look at the section "Store your photos and videos in iCloud" in this support article:--> Manage your photo and video storage - Apple Support, and optimize your storage

or, even better, take into consideration to copy/archive your photos/videos on a computer (using this procedure:--> Archive or make copies of the information you store in iCloud - Apple Support

When your media or other stuff are safely stored on your computer, you can delete some of them from your iPad (or from iCloud) to make more room.

Regards

Giulio