Saving storage space on iPad via Review Large Attachments

It is generally recommended that you maintain 4-6GB of free space at all times - as your iPad needs some temporary space to complete some tasks - such as performing system software updates.

If your internal storage is full, or is insufficient for the task that you need to perform, 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

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

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

Additional information about creating sufficient space for installation of a software update can be found here:

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

External storage options can often help with managing limited internal storage. Depending upon your iPad model, the iPad will either have a Lightning or USB-C port - and may therefore require either an Adapter or USB hub to connect the USB Storage device. If your iPad has a Lightning port, you’ll need an Apple Lightning to USB3 Camera Adapter:

• Lightning to USB 3 Camera Adapter

https://store.apple.com/uk/xc/product/MK0W2ZM/A

j9lemmon wrote:

Thanks LotusPilot & sberman for your replies.

I hadn't realized that it's best to keep 4-6 GB free on an iPad.

I was able to get to about 8 GB free on my iPad.

At least 4-6GB is recommended - although keeping more available will help you download and install larger update packages without running-out of space for temporary files.

When performing an OTA update directly from iPad/iPhone settings, a good rule-of-thumb is to ensure that you have double the space that the update itself requires. Remember, an update must be downloaded, unpacked and verified before it can be installed - requiring more space than the update itself.

If performing an update using a Windows PC or Mac computer, the update is first downloaded and prepared by the host computer. Once unpacked and verified on the computer, the update is installed by the computer on the iPad/iPhone. This process requires somewhat less free space to be available on the device being updated.

See this article.

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