Cubase Elements is an higher edition than Cubase AI. So it’s more downgrade than upgrade.
In any case, you don’t have to uninstall Cubase Elements. Cubase Elements and AI share the same installer and executable. So you can just activate your Cubase AI. Once the Cubase Elements Trial license will be over, it will switch to Cubase AI automatically.
Download the Driver and the tools from Steinberg sides, please.