Mac Pro memory

Depending on the model and macOS installed on your Mac "Storage is full" means

built in HD/SSD is running out of storage space.

For what a user can do about it, please read this article.

https://support.apple.com/en-us/HT206996

RAM

Please this list.

https://support.apple.com/en-us/HT201165

If your reference is to Storage( Hard Drive,Disk) you have to contact a third party vendor like OWC.

There are many other vendors like that.

https://eshop.macsales.com/Service/sales_request.cfm