NOT ENOUGH MEMORY TO UPDATE

Generally, if the device is disabled, it's not a problem of memory. Most likely it's due to too many unsuccessful attempts to input the correct passcode. Should be this case:

Given that to remove the existing passcode you must connect your device via USB to a computer (a Windows PC running the latest iTunes version, or a Mac, which can run iTunes or Finder, depending on the macOS installed on it), and keeping in mind that if you don't have a backup all data will be lost on that device (except those that you eventually synced to iCloud), pay attention to the specific gestures that you need to perform while connecting your device to the computer.

These are the instructions to re-gain access to your iPhone/iPad:

If it is an iPhone:--> If you forgot your iPhone passcode - Apple Support

If it is an iPad:--> If you forgot the passcode on your iPad, or your iPad is disabled - Apple Support

Or, watch this support video about the same matter (for both iPhone and iPad):

https://www.youtube.com/watch?v=7s8-zLG9ySQ

If you mean something different, please better specify your needs.

Regards

Giulio

An iPad passcode cannot be reset or modified from another device. If your iPad is disabled, or you have forgotten your iPad passcode, you have no alternative other than to follow this process:

If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support

You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

Use of a PC or Mac is unavoidable. If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store will be delighted to assist.

You may also need your AppleID and associated password. If these have also been forgotten, they can be recovered here:

https://iforgot.apple.com

To recover your credentials, you’ll need access to one of the following:

• Your primary email address mailbox that corresponds with your AppleID
• Any of the secondary/recovery email addresses that should be configured for your AppleID account
• Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID

Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.

More information about recovery of your AppleID:

If you forgot your Apple ID - Apple Support

More information about recovery of your AppleID password:

If you forgot your Apple ID password - Apple Support

When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:

https://appleid.apple.com

In addressing your additional problem - concerning available storage to perform an update - 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:

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 the software update.

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