upgrade memory on ipad pro model A1764

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. 

You can, however, subscribe to a higher tier of iCloud storage - but this is not a substitute for internal storage.

About storage on your device and in iCloud – Apple Support

Manage your iCloud storage – Apple Support

If you have insufficient internal storage for your needs, you have two options:

• Manage the storage that you already have:

How to check the storage on your iPhone, iPad and iPod touch – Apple Support

• Replace your iPad with a model with adequate storage for your needs.

Yes, connection of external storage devices is possible - with some caveats...

To be recognised by iPadOS, the attached USB storage device must be formatted to FAT, FAT32, exFAT, APFS or HFS+ with a single partition. As the iPad has limited power capabilities, dependent upon the Storage Device, an external power source is often required.

If your iPad Pro has a Lightning port, you will need to use an Apple Lightning to USB3 Camera Adapter to directly connect USB devices to the iPad. This adapter has both a USB 3.0 Type-A connector and an additional Lightning port to supply power, from your Power Adapter, to both the iPad and connected device. The external Power Adapter must be rated at 12W or more.

If you have one of the newest iPad Pro models, with a USB-C connector, you may need to utilise a powered USB hub (i.e., it has its own source of power) - connecting both the iPad Pro and the storage device to ports on the hub.

Some additional information can be found here:

Connect external devices or servers with Files on iPhone - Apple Support

https://www.imore.com/how-use-external-hard-drives-your-iphone-or-ipad

I hope this is helpful.