It is impossible to increase the amount of RAM or internal storage in your iPad - as this is fixed during manufacture; what you have is fixed for the life of your device.
64GB storage really isn't much. iPadOS itself will occupy ~10GB of total space. Cached data may typically occupy another 10+GB, plus you need to maintain 4-6GB of free space for normal functioning of your iPad. This alone is going on for half of the total device storage of your iPad.
While you can subscribe to iCloud storage - this is not necessarily a substitute for internal storage.
Upgrade to iCloud+ - Apple Support
Synchronising files and photos to iCloud creates a copy of the synchronised data - allowing this data to be synchronised between devices; if synchronised data is deleted from a device, the iCloud copy is also deleted. iCloud backup data is similarly a backup of the device itself; if data is deleted from the iPad, the backup data is similarly deleted when the backup is next refreshed.
You can, however, manually move files to iCloud storage - this data then being independent of the device. As such, your iPad and iCloud storage needn't have the same files.
If your internal storage is full, your only option is to better manage the storage that you have - and delete unused Apps or move 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