Regrettably, you are always going to struggle with an iPad that has so little internal storage. The 32/64GB devices are primarily intended for use in Educational settings, or in environments where the ability to store local data on the device is not required.
Using a Mac computer or Windows PC can help with system software updates - as the update package is initially downloaded to the computer, unpacked and verified by the computer, prior to the computer installing the updated system software on the target device.
As is, perhaps a workable remedy is to ensure that you have either an iCloud or iTunes backup of your iPad - and then completely erase the iPad. With no user-data present, you should be able to update the iPad; once updated, you can restore your backup to the iPad.
How to back up your iPhone, iPad, and iPod touch - Apple Support
Erase all content and settings:
Settings > General > Transfer or Reset iPad > Erase All Content & Settings
After the reset, set-up the iPad with your AppleID - but do not restore the backup. Perform the system software update using whichever method works for you.
Finally, restore the backup to your iPad:
Restore all content to iPad from a backup - Apple Support