How do I update iPadOS when iPad storage is full?

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 you have inadequate space, you may be able to use a Windows PC or Mac computer to perform the update, this method potentially requiring less free space to be available on the iPad.

A system software update requires sufficient space to be downloaded, unpacked and verified prior to installation - major version updates (such as updating from iPadOS 16.x to iPadOS 17) requiring considerably more space than an incremental point-update. After the update is successfully completed, temporary files are automatically deleted - returning free space.

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

Updating your iPad using a Windows PC (with iTunes for Windows - or more recent Apple Devices App) or a Mac computer (with iTunes or Finder - as appropriate for the installed version of macOS) can reduce the amount of free-space necessary to perform the update - as the initial download, unpacking and verification is performed on the computer prior to installation. However, even this method is not possible if your iPad has too little free space.

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Apple Devices App (Windows PC):

https://apps.microsoft.com/detail/9np83lwlpz9k?hl=en-ms&gl=MS