When you switch to Video from Camera, you will see the resolutions and frame rates on top of the camera's viewfinder.
To see what your options are, tap the third icon from the right at the top of the screen. You can change the resolution and file size by using the second icon from the right.
If you need to quickly clear out some storage space on your local device, you can tap your profile picture and choose free up space from inside the app. The app will let you know how much space you freed up when you deleted photos and videos that were safely backed up.
There is an operating system for the iPad
The camera quality settings can be accessed if you open the settings screen and tap the camera then formats. If you want to keep file sizes as low as possible, you can choose High Efficiency instead of Most Compatible, which will use Apple's preferred HEIF/HEVC formats rather than the more standard JPEG/H.264 ones.
You can see Apple ProRAW and Apple ProRes under the resolution options on the model of the phone you use. To enable or disabling these modes, you need to do it from the shutter screen when you launch the camera.
You can change the resolution and frame rate of your video on the camera options screen. The resolution and frame rate that take up the least amount of room will be listed first.
When it comes to saving space on your phone, there is one more option that you should mention. If your images and videos are being backed up to iCloud and there isn't a lot of room left on your device, you'll be able to save space with lower resolution copies of your files locally.